<html><head></head><body dir="auto" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><meta http-equiv="Content-Type" content="text/html charset=utf-8"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Hello everyone!</div><div class=""><br class=""></div><div class="">Here is a draft proposal to fill in some usability gaps in the standard library Dictionary and Set types. I'd love to hear any feedback from the list before submitting this as a PR.</div><div class=""><br class=""></div><div class="">Thanks!</div><div class="">Nate</div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class="">Dictionary & Set Enhancements</h1><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class=""><li style="box-sizing: border-box;" class="">Proposal: <a href="" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">SE-0000</a></li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Author: <a href="https://github.com/natecook1000" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">Nate Cook</a></li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Review Manager: TBD</li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Status: <span style="box-sizing: border-box; font-weight: 600;" class="">Awaiting review</span></li></ul></h1><h2 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-introduction" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#introduction" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>Introduction</h2><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">This proposal comprises a variety of commonly (and less commonly) suggested improvements to the standard library's <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code> type, from merging initializers to dictionary-specific <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">filter</code> and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">mapValues</code> methods. The proposed additions to <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code>, and the corresponding changes to <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Set</code>, are detailed in the sections below.</p><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class=""><li style="box-sizing: border-box;" class="">Suggested Improvements:<ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 0px;" class=""><li style="box-sizing: border-box;" class=""><a href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#1-merging-initializers-and-methods" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">Merging initializers and methods</a></li><li style="box-sizing: border-box; margin-top: 0.25em;" class=""><a href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#2-key-based-subscript-with-default-value" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">Key-based subscript with default value</a></li><li style="box-sizing: border-box; margin-top: 0.25em;" class=""><a href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#3-dictionary-specific-map-and-filter" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">Dictionary-specific map and filter</a></li><li style="box-sizing: border-box; margin-top: 0.25em;" class=""><a href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#4-visible-dictionary-capacity" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">Visible <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code> capacity</a></li><li style="box-sizing: border-box; margin-top: 0.25em;" class=""><a href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#5-dictionaryremoveat-returns-next-index" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class=""><code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary.remove(at:)</code> returns next index</a></li><li style="box-sizing: border-box; margin-top: 0.25em;" class=""><a href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#6-a-groupedby-method-for-sequences" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">A <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">grouped(by:)</code> method for sequences</a></li><li style="box-sizing: border-box; margin-top: 0.25em;" class=""><a href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#7-apply-relevant-changes-to-set" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">Relevant changes to <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Set</code></a></li></ul></li><li style="box-sizing: border-box; margin-top: 0.25em;" class=""><a href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#detailed-design" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">Detailed Design</a><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 0px;" class=""><li style="box-sizing: border-box;" class=""><a href="http://swift.sandbox.bluemix.net/#/repl/58daf2d4ecbff41fe22d681a" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">Sandbox with Prototype</a></li></ul></li><li style="box-sizing: border-box; margin-top: 0.25em;" class=""><a href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#source-compatibility" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">Source Compatibility</a></li></ul><hr style="box-sizing: content-box; height: 0.25em; overflow: hidden; margin: 24px 0px; background-color: rgb(225, 228, 232); border: 0px; padding: 0px; font-size: 16px; font-weight: normal;" class=""></h1><h2 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-1-merging-initializers-and-methods" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#1-merging-initializers-and-methods" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>1. Merging initializers and methods</h2><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">The <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code> type should allow initialization from a sequence of <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">(Key, Value)</code> tuples and offer methods that merge a sequence of <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">(Key, Value)</code> tuples into a new or existing dictionary, using a closure to combine values for duplicate keys.</p><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class=""><li style="box-sizing: border-box;" class=""><a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160104/006124.html" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">First message of discussion thread</a></li><li style="box-sizing: border-box; margin-top: 0.25em;" class=""><a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160111/006665.html" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">Initial proposal draft</a></li><li style="box-sizing: border-box; margin-top: 0.25em;" class=""><a href="https://github.com/apple/swift-evolution/blob/master/proposals/0100-add-sequence-based-init-and-merge-to-dictionary.md" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">Prior standalone proposal (SE-100)</a></li></ul><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class=""><code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Array</code> and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Set</code> both have initializers that create a new instance from a sequence of elements. The <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Array</code> initializer is useful for converting other sequences and collections to the "standard" collection type, while the <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Set</code> initializer is essential for recovering set operations after performing any functional operations on a set. For example, filtering a set produces a collection without any set operations available.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> numberSet <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Set</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">...</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">100</span>)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> fivesOnly <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> numberSet.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">lazy</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">filter</span> { <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">$0</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">%</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">5</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">==</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">0</span> }</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class=""><code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">fivesOnly</code> is a <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">LazyFilterCollection<Set<Int>></code> instead of a <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Set</code>—sending that back through the <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Set</code> sequence initializer restores the expected methods.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> fivesOnlySet <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Set</span>(numberSet.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">lazy</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">filter</span> { <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">$0</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">%</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">5</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">==</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">0</span> })
fivesOnlySet.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">isSubsetOf</span>(numberSet) <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> true</span></pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class=""><code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code>, on the other hand, has no such initializer, so a similar operation leaves no room to recover dictionary functionality without building a mutable <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code> via iteration or functional methods. These techniques also don't support type inference from the source sequence, increasing verbosity.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> numberDictionary <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> [<span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>one<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>two<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">2</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>three<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">3</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>four<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">4</span>]
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> evenOnly <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> numberDictionary.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">lazy</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">filter</span> { (<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">_</span>, value) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">in</span>
value <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">%</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">2</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">==</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">0</span>
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> viaIteration<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> [<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">String</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> [<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span>]
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">for</span> (key, value) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">in</span> evenOnly {
viaIteration[key] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> value
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> viaReduce<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> [<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">String</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> evenOnly.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">reduce</span>([<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span>]) { (cumulative, kv) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">in</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> dict <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> cumulative
dict[kv.<span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">key</span>] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> kv.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">value</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> dict
}</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">Beyond initialization, <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Array</code> and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Set</code> both also provide a method to add a new block of elements to an existing collection. <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Array</code> provides this via <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">append(contentsOf:)</code> for the common appending case or <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">replaceSubrange(_:with:)</code> for general inserting or replacing, while the unordered <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Set</code> type lets you pass any sequence to <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">unionInPlace(_:)</code> to add elements to an existing set.</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">Once again, <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code> has no corresponding API -- looping and adding elements one at a time as shown above is the only way to merge new elements into an existing dictionary.</p></h1><h3 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; font-size: 1.25em; line-height: 1.25; color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-proposed-solution" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#proposed-solution" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>Proposed solution</h3><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">This proposal puts forward two new ways to convert <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">(Key, Value)</code> sequences to dictionary form: a full-width, failable initializer and a set of merging APIs that handle input data with duplicate keys.</p></h1><h4 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; font-size: 16px; line-height: 1.25; color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-sequence-based-initializer" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#sequence-based-initializer" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>Sequence-based initializer</h4><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">The proposed solution would add a new, failable initializer to <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code> that accepts any sequence of <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">(Key, Value)</code>tuple pairs.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init?</span><<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">S</span>: <span class="pl-e" style="box-sizing: border-box; color: rgb(121, 93, 163);"><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Sequence</span> </span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">where</span> S.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Iterator</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">==</span> (key: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Key</span>, value: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>)>(
<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">keysAndValues</span>: S)</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">Instead of the techniques for recovering a <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code> instance shown above, the proposed initializer would allow a much cleaner syntax.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> viaProposed <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Dictionary</span>(evenOnly)<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">!</span></pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">Like <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Array.init(_:)</code> and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Set.init(_:)</code>, this is a full-width initializer. To ensure this, the initializer requires that each key in the supplied sequence is unique, and returns <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">nil</code> whenever that condition isn't met. This model prevents accidentally dropping values for keys that might be duplicated, but allows easier recovery than the trap that results from duplicate keys in a dictionary literal.</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">The new initializer allows for some convenient uses that aren't currently possible.</p><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class=""><li style="box-sizing: border-box;" class=""><p style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;" class="">Initializing from a <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">DictionaryLiteral</code> (the type, not an actual literal)</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> literal<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">DictionaryLiteral</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> [<span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>a<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>b<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">2</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>c<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">3</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>d<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">4</span>]
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> dictFromDL <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Dictionary</span>(literal)<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">!</span></pre></div></li><li style="box-sizing: border-box; margin-top: 0.25em;" class=""><p style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;" class="">Swapping keys and values of an existing dictionary</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">guard</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> reversedDict <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Dictionary</span>(dictFromDL.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">map</span> { (<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">$1</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">$0</span>) })
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">else</span> { <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">throw</span> Errors.<span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">reversalFailed</span> }
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> [2: "b", 4: "d", 1: "a", 3: "c"]</span></pre></div></li><li style="box-sizing: border-box; margin-top: 0.25em;" class=""><p style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;" class="">Converting an array to an indexed dictionary (popular on the thread)</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> names <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> [<span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>Cagney<span class="pl-pds" style="box-sizing: border-box;">"</span></span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>Lacey<span class="pl-pds" style="box-sizing: border-box;">"</span></span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>Bensen<span class="pl-pds" style="box-sizing: border-box;">"</span></span>]
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> dict <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Dictionary</span>(names.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">enumerated</span>().<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">map</span> { (i, val) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">in</span> (i <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">+</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>, val) })<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">!</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> [2: "Lacey", 3: "Bensen", 1: "Cagney"]</span></pre></div></li><li style="box-sizing: border-box; margin-top: 0.25em;" class=""><p style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;" class="">Initializing from a pair of zipped sequences (examples abound)</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> letters <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>abcdef<span class="pl-pds" style="box-sizing: border-box;">"</span></span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">characters</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">lazy</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">map</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">String</span>.<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> dictFromZip <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Dictionary</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">zip</span>(letters, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">...</span><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">10</span>))<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">!</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> ["b": 2, "e": 5, "a": 1, "f": 6, "d": 4, "c": 3]</span></pre></div><blockquote style="box-sizing: border-box; margin: 0px 0px 16px; padding: 0px 1em; color: rgb(106, 115, 125); border-left-width: 0.25em; border-left-style: solid; border-left-color: rgb(223, 226, 229);" class=""><div style="box-sizing: border-box; margin-top: 0px; margin-bottom: 0px;" class="">This particular use is currently blocked by <a href="https://bugs.swift.org/browse/SR-922" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">SR-922</a>. As a workaround, add <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">.map {(key: $0, value: $1)}</code>.</div></blockquote></li></ul></h1><h4 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; font-size: 16px; line-height: 1.25; color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-merging-initializer-and-methods" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#merging-initializer-and-methods" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>Merging initializer and methods</h4><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">Creating a <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code> from a dictional literal currently checks the keys for uniqueness, trapping on a duplicate. The sequence-based initializer shown above has the same requirements, failing and returning <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">nil</code> when encountering duplicate keys.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> duplicates<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">DictionaryLiteral</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> [<span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>a<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>b<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">2</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>a<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">3</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>b<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">4</span>]
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> letterDict <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Dictionary</span>(duplicates)
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> nil</span></pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">However, some use cases can be forgiving of duplicate keys, so this proposal includes a second new initializer. This initializer allows the caller to supply, along with the sequence, a combining closure that's called with the old and new values for any duplicate keys.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span><<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">S</span>: <span class="pl-e" style="box-sizing: border-box; color: rgb(121, 93, 163);"><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Sequence</span></span>>(
<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">merging</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">keysAndValues</span>: S,
<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">resolvingCollisionsWith</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">combine</span>: (<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">throws</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>
) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">rethrows</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">where</span> S.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Iterator</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">==</span> (key: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Key</span>, value: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>)</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">This example shows how one could keep the first value of all those supplied for a duplicate key.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> letterDict2 <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Dictionary</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">merging</span>: duplicates, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">resolvingCollisionsWith</span>: { (first, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">_</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">in</span> first })
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> ["b": 2, "a": 1]</span></pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">Or the largest value for any duplicate keys.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> letterDict3 <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Dictionary</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">merging</span>: duplicates, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">resolvingCollisionsWith</span>: max)
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> ["b": 4, "a": 3]</span></pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">At other times the merging initializer could be used to combine values for duplicate keys. Donnacha Oisín Kidney wrote a neat <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">frequencies()</code> method for sequences as an example of such a use in the thread.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">extension</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);"><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Sequence</span></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">where</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Iterator</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-e" style="box-sizing: border-box; color: rgb(121, 93, 163);"><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Hashable</span></span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">frequencies</span>() <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> [<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Iterator</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>] {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Dictionary</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">merging</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">self</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">lazy</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">map</span> { v <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">in</span> (v, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>) }, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">resolvingCollisionsWith</span>: <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">+</span>)
}
}
[<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">2</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">2</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">3</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">2</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">4</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">5</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">3</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">2</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">3</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>].<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">frequencies</span>()
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> [2: 4, 4: 1, 5: 1, 3: 3, 1: 3]</span></pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">This proposal also includes new mutating and non-mutating methods for <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code> that merge the contents of a sequence of <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">(Key, Value)</code> tuples into an existing dictionary, <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">merge(contentsOf:)</code> and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">merged(with:)</code>.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">mutating</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">merge</span><<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">S</span>: <span class="pl-e" style="box-sizing: border-box; color: rgb(121, 93, 163);"><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Sequence</span></span>>(
<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">contentsOf</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">other</span>: S,
<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">resolvingCollisionsWith</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">combine</span>: (<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">throws</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>
) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">rethrows</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">where</span> S.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Iterator</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">==</span> (key: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Key</span>, value: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">merged</span><<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">S</span>: <span class="pl-e" style="box-sizing: border-box; color: rgb(121, 93, 163);"><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Sequence</span></span>>(
<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">with</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">other</span>: S,
<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">resolvingCollisionsWith</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">combine</span>: (<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">throws</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>
) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">rethrows</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> [<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Key</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">where</span> S.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Iterator</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">==</span> (key: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Key</span>, value: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>)</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">As above, there are a wide variety of uses for the merge.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> Adding default values</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> defaults<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> [<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">String</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Bool</span>] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> [<span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>foo<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">false</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>bar<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">false</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>baz<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">false</span>]
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> options<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> [<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">String</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Bool</span>] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> [<span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>foo<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">true</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>bar<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">false</span>]
options.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">merge</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">contentsOf</span>: defaults) { (old, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">_</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">in</span> old }
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> options is now ["foo": true, "bar": false, "baz": false]</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> Summing counts repeatedly</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> bugCounts<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> [<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">String</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> [<span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>bees<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">9</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>ants<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">112</span>, <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">...</span>]
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">while</span> bugCountingSource.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">hasMoreData</span>() {
bugCounts.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">merge</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">contentsOf</span>: bugCountingSource.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">countMoreBugs</span>(), <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">resolvingCollisionsWith</span>: <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">+</span>)
}</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">To simplify two common uses of the merging initializer, this proposal includes the addition of two new top-level functions to the standard library: <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">first(_:_:)</code> and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">last(_:_:)</code>, which return their first and last arguments, respectively. These new functions can be passed instead of a custom closure:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> firstWins <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Dictionary</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">merging</span>: duplicates, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">resolvingCollisionsWith</span>: first)
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> ["b": 2, "a": 1]</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> lastWins <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Dictionary</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">merging</span>: duplicates, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">resolvingCollisionsWith</span>: last)
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> ["b": 4, "a": 3]</span></pre></div></h1><h3 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; font-size: 1.25em; line-height: 1.25; color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-alternatives-considered" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#alternatives-considered" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>Alternatives Considered</h3><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">The <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">first(_:_:)</code> and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">last(_:_:)</code> functions may not pull their weight as top-level symbols. Instead, at the cost of additional overloads for the merging initializer and methods, we could allow users to specify the <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">useFirst</code> and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">useLast</code> cases of a <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">MergeCollisionStrategy</code> enumeration.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">extension</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);"><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Dictionary</span></span> {
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> The strategy to use when merging a sequence of key-value pairs into a dictionary.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">enum</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">MergeCollisionStrategy</span> {
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> If there is more than one instance of a key in the sequence to merge, use</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> only the first value for the dictionary.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">useFirst</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> If there is more than one instance of a key in the sequence to merge, use</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> only the last value for the dictionary.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">useLast</span>
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span><<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">S</span>: <span class="pl-e" style="box-sizing: border-box; color: rgb(121, 93, 163);"><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Sequence</span></span>>(
<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">merging</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">keysAndValues</span>: S,
<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">resolvingCollisionsWith</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">strategy</span>: MergeCollisionStrategy
)
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> other merging overloads</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span>}</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">In use, this overload would look similar to the functional version, but may aid in discoverability:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> firstWins <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Dictionary</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">merging</span>: duplicates, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">resolvingCollisionsWith</span>: .<span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">useFirst</span>)
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> ["b": 2, "a": 1]</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> lastWins <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Dictionary</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">merging</span>: duplicates, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">resolvingCollisionsWith</span>: .<span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">useLast</span>)
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> ["b": 4, "a": 3]</span></pre></div><hr style="box-sizing: content-box; height: 0.25em; overflow: hidden; margin: 24px 0px; background-color: rgb(225, 228, 232); border: 0px; padding: 0px; font-size: 16px; font-weight: normal;" class=""></h1><h2 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-2-key-based-subscript-with-default-value" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#2-key-based-subscript-with-default-value" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>2. Key-based subscript with default value</h2><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">Another common challenge with dictionaries is iteratively making changes to key/value pairs that may or may not already be present. For example, to iteratively add count the frequencies of letters in a string, one might write something like the following:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> source <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>how now brown cow<span class="pl-pds" style="box-sizing: border-box;">"</span></span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> frequencies<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> [<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Character</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> [<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span>]
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">for</span> c <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">in</span> source.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">characters</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">if</span> frequencies[c] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">==</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">nil</span> {
frequencies[c] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>
} <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">else</span> {
frequencies[c]<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">!</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">+=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>
}
}</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">Testing for <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">nil</code> and assigning through the force unwrapping operator are awkward at best for such a common operation. Furthermore, the <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Optional<Value></code> return type of the current keyed subscript complicates efficiencies that could be gained for this type of <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">modify</code> action under a future ownership model.</p></h1><h3 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; font-size: 1.25em; line-height: 1.25; color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-proposed-solution-1" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#proposed-solution-1" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>Proposed solution</h3><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">A keyed subscript with a default value neatly simplifies this usage. Instead of checking for <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">nil</code>, one can pass the default value along with the key as a <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">default</code> subscript parameter.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> source <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>how now brown cow<span class="pl-pds" style="box-sizing: border-box;">"</span></span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> frequencies<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> [<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Character</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> [<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span>]
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">for</span> c <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">in</span> source.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">characters</span> {
frequencies[c, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">default</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">0</span>] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">+=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>
}</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">The return type of this subscript is a non-optional <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Value</code>. Note that accessing the subscript as a getter never stores the default value in the dictionary—the following two lines are equivalent:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> x <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> frequencies[<span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>a<span class="pl-pds" style="box-sizing: border-box;">"</span></span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">default</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">0</span>]
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> y <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> frequencies[<span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>a<span class="pl-pds" style="box-sizing: border-box;">"</span></span>] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">??</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">0</span></pre></div><hr style="box-sizing: content-box; height: 0.25em; overflow: hidden; margin: 24px 0px; background-color: rgb(225, 228, 232); border: 0px; padding: 0px; font-size: 16px; font-weight: normal;" class=""></h1><h2 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-3-dictionary-specific-map-and-filter" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#3-dictionary-specific-map-and-filter" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>3. Dictionary-specific map and filter</h2><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">The standard <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">map</code> and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">filter</code> methods, while always useful and beloved, aren't ideal when applied to dictionaries. In both cases, the desired end-result is frequently another dictionary instead of an array of key-value pairs—even with the sequence-based initializer proposed above this is an inefficient way of doing things.</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">Additionally, the standard <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">map</code> method doesn't gracefully support passing a function when transforming only the <em style="box-sizing: border-box;" class="">values</em> of a dictionary. The transform function must accept and return key/value pairs, necessitating a custom closure in nearly every case.</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">Assuming the addition of a sequence-based initializer, the current <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">filter</code> and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">map</code> look like the following:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> numbers <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> [<span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>one<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>two<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">2</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>three<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">3</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>four<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">4</span>]
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> evens <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Dictionary</span>(numbers.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">lazy</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">filter</span> { <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">$0</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">value</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">%</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">2</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">==</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">0</span> })<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">!</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> ["four": 4, "two": 2]</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> strings <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Dictionary</span>(numbers.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">lazy</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">map</span> { (k, v) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">in</span> (k, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">String</span>(v)) })<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">!</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> ["three": "3", "four": "4", "one": "1", "two": "2"]</span></pre></div></h1><h3 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; font-size: 1.25em; line-height: 1.25; color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-proposed-solution-2" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#proposed-solution-2" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>Proposed solution</h3><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">This proposal adds two new methods for <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code>:</p><ol style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class=""><li style="box-sizing: border-box;" class=""><p style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;" class="">A <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">mapValues</code> method that keeps a dictionary's keys intact while transforming the values. Mapping a dictionary's key/value pairs can't always produce a new dictionary, due to the possibility of key collisions, but mapping only the values can produce a new dictionary with the same underlying layout as the original.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> strings <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> numbers.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">mapValues</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">String</span>.<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>)
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> ["three": "3", "four": "4", "one": "1", "two": "2"]</span></pre></div></li><li style="box-sizing: border-box; margin-top: 0.25em;" class=""><p style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;" class="">A <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code>-returning <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">filter</code> method. While transforming the keys and values of a dictionary can result in key collisions, filtering the elements of a dictionary can at worst replicate the entire dictionary.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> evens <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> numbers.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">filter</span> { <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">$0</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">value</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">%</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">2</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">==</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">0</span> }
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> ["four": 4, "two": 2]</span></pre></div></li></ol><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">Both of these can be made significantly more efficient than their <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Sequence</code>-sourced counterparts. For example, the <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">mapValues</code> method can simply copy the portion of the storage that holds the keys to the new dictionary before transforming the values.</p><hr style="box-sizing: content-box; height: 0.25em; overflow: hidden; margin: 24px 0px; background-color: rgb(225, 228, 232); border: 0px; padding: 0px; font-size: 16px; font-weight: normal;" class=""></h1><h2 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-4-visible-dictionary-capacity" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#4-visible-dictionary-capacity" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>4. Visible dictionary capacity</h2><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">As you add elements to a dictionary, it automatically grows its backing storage as necessary. This reallocation is a significant operation—unlike arrays, where the existing elements can be copied to a new block of storage en masse, every key/value pair must be moved over individually, recalculating the hash value for the key to find its position in the larger backing buffer.</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">While dictionaries uses an exponential growth strategy to make this as efficient as possible, beyond the <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">init(minimumCapacity:)</code> initializer they do not expose a way to reserve a specific capacity. In addition, adding a key/value pair to a dictionary is guaranteed not to invalidate existing indices as long as the capacity doesn't change, yet we don't provide any way of seeing a dictionary's current or post-addition capacity.</p></h1><h3 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; font-size: 1.25em; line-height: 1.25; color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-proposed-solution-3" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#proposed-solution-3" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>Proposed solution</h3><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class=""><code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code> should add a <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">capacity</code> property and a <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">reserveCapacity(_:)</code> method, like those used in range-replaceable collections. The <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">capacity</code> of a dictionary is the number of elements it can hold without reallocating a larger backing storage, while calling <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">reserveCapacity(_:)</code> allocates a large enough buffer to hold the requested number of elements without reallocating.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> numbers <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> [<span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>one<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>two<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">2</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>three<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">3</span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>four<span class="pl-pds" style="box-sizing: border-box;">"</span></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">4</span>]
numbers.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">capacity</span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> 6</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span>numbers.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">reserveCapacity</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">20</span>)
numbers.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">capacity</span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> 24</span></pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">Because hashed collections use extra storage capacity to reduce the likelihood and cost of collisions, the value of the <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">capacity</code> property won't be equal to the actual size of the backing storage. Likewise, the capacity after calling <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">reserveCapacity(_:)</code> will be at least as large as the argument, but usually larger. (In its current implementation, <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code> always has a power of 2-sized backing storage.)</p><hr style="box-sizing: content-box; height: 0.25em; overflow: hidden; margin: 24px 0px; background-color: rgb(225, 228, 232); border: 0px; padding: 0px; font-size: 16px; font-weight: normal;" class=""></h1><h2 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-5-dictionaryremoveat-returns-next-index" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#5-dictionaryremoveat-returns-next-index" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>5. <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: inherit; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary.remove(at:)</code> returns next index</h2><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">The method dictionaries use to store their key/value pairs can make it challenging to sequentially remove elements in an efficient way. To demonstrate, considering the following hypothetical dictionary:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> dict <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Dictionary</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Bool</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">minimumCapacity</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">5</span>)
dict[<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">3</span>] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">true</span>
dict[<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">7</span>] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">true</span>
dict[<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">false</span></pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">To add those three elements, <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">dict</code> performs the following steps:</p><ol style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class=""><li style="box-sizing: border-box;" class="">Uses <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">3.hashValue</code> to select a bucket, choosing bucket <span style="box-sizing: border-box; font-weight: 600;" class="">5</span>.</li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Stores <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">3</code> and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">true</code> at position <span style="box-sizing: border-box; font-weight: 600;" class="">5</span> in the key and value storage, respectively.</li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Uses <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">7.hashValue</code> to select a bucket, choosing bucket <span style="box-sizing: border-box; font-weight: 600;" class="">2</span>.</li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Stores <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">7</code> and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">true</code> at position <span style="box-sizing: border-box; font-weight: 600;" class="">2</span>.</li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Uses <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">1.hashValue</code> to select a bucket, choosing bucket <span style="box-sizing: border-box; font-weight: 600;" class="">5</span>. <em style="box-sizing: border-box;" class="">Collision!</em> Advances to the next open space, bucket <span style="box-sizing: border-box; font-weight: 600;" class="">6</span>.</li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Stores <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">1</code> and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">false</code> at position <span style="box-sizing: border-box; font-weight: 600;" class="">6</span>.</li></ol><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">With these three elements, we have a storage layout depicted by the table below—<code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">7</code> and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">3</code> are in their ideal buckets, but <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">1</code> is not:</p><table style="box-sizing: border-box; border-spacing: 0px; border-collapse: collapse; margin-top: 0px; margin-bottom: 16px; display: block; width: 888px; overflow: auto; color: rgb(36, 41, 46); font-size: 16px;" class=""><thead style="box-sizing: border-box;" class=""><tr style="box-sizing: border-box; border-top-width: 1px; border-top-style: solid; border-top-color: rgb(198, 203, 209);" class=""><th style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class=""><em style="box-sizing: border-box;" class="">bucket</em></th><th style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class="">0</th><th style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class="">1</th><th style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class="">2</th><th style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class="">3</th><th style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class="">4</th><th style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class="">5</th><th style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class="">6</th><th style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class="">7</th></tr></thead><tbody style="box-sizing: border-box;" class=""><tr style="box-sizing: border-box; border-top-width: 1px; border-top-style: solid; border-top-color: rgb(198, 203, 209);" class=""><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class=""><em style="box-sizing: border-box;" class="">key</em></td><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class=""></td><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class=""></td><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class="">7</td><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class=""></td><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class=""></td><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class="">3</td><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class="">1</td><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class=""></td></tr><tr style="box-sizing: border-box; background-color: rgb(246, 248, 250); border-top-width: 1px; border-top-style: solid; border-top-color: rgb(198, 203, 209);" class=""><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class=""><em style="box-sizing: border-box;" class="">value</em></td><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class=""></td><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class=""></td><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class="">T</td><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class=""></td><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class=""></td><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class="">T</td><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class="">F</td><td style="box-sizing: border-box; padding: 6px 13px; border: 1px solid rgb(223, 226, 229);" class=""></td></tr></tbody></table><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">To write an algorithm that removes each element from the dictionary, we would want to do something like this:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> i <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> dict.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">startIndex</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">while</span> i <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">!=</span> dict.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">endIndex</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> next <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> dict.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">index</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">after</span>: i)
dict.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">remove</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">at</span>: i)
i <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> next
}</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">This will remove <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">(7, true)</code> without incident, but when it removes <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">(3, true)</code>, the dictionary will need to shift <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">(1, false)</code>back one slot so that it is found in bucket 5. This shift will invalidate the <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">next</code> index that has already been calculated. With the current index invalidation rules, there's no way to do this efficiently.</p></h1><h3 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; font-size: 1.25em; line-height: 1.25; color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-proposed-solution-4" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#proposed-solution-4" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>Proposed solution</h3><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">If the <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">remove(at:)</code> method returns the next valid index, this kind of algorithm is possible. <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">remove(at:)</code> already returns the key/value pair that was removed, so this would change the return type to a tuple:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">@discardableResult</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">mutating</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">remove</span>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">at</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">index</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Index</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span>
(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">removed</span>: (<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">key</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Key</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">value</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>), <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">nextIndex</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Index</span>)</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">The code above can be rewritten as the following. When <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">(1, false)</code> is shifted back into bucket 5, there is no problem, since the method can return that same index.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> i <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> dict.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">startIndex</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">while</span> i <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">!=</span> dict.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">endIndex</span> {
(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">_</span>, i) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> dict.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">remove</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">at</span>: i)
}</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">This new capability could be used to implement an efficient in-place filter.</p><hr style="box-sizing: content-box; height: 0.25em; overflow: hidden; margin: 24px 0px; background-color: rgb(225, 228, 232); border: 0px; padding: 0px; font-size: 16px; font-weight: normal;" class=""></h1><h2 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-6-a-groupedby-method-for-sequences" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#6-a-groupedby-method-for-sequences" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>6. A <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: inherit; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">grouped(by:)</code> method for sequences</h2><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">As a final <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code>-related issue, grouping elements in a sequence by some computed key is a commonly requested addition that we can add as part of this omnibus proposal. Pass a closure that converts each value in a sequence to a hashable type <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">T</code>; the result of the method is a dictionary with keys of type <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">T</code> and values of type <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">[Iterator.Element]</code>.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> names <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> [<span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>Patti<span class="pl-pds" style="box-sizing: border-box;">"</span></span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>Aretha<span class="pl-pds" style="box-sizing: border-box;">"</span></span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>Anita<span class="pl-pds" style="box-sizing: border-box;">"</span></span>, <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>Gladys<span class="pl-pds" style="box-sizing: border-box;">"</span></span>]
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> By first letter</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span>names.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">grouped</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">by</span>: { <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">$0</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">characters</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">first</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">!</span> })
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> ["P": ["Patti"], "G": ["Gladys"], "A": ["Aretha", "Anita"]]</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> By name length</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span>names.<span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">grouped</span> { <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">$0</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">utf16</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">count</span> }
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> [5: ["Patti", "Anita"], 6: ["Aretha", "Gladys"]]</span></pre></div><hr style="box-sizing: content-box; height: 0.25em; overflow: hidden; margin: 24px 0px; background-color: rgb(225, 228, 232); border: 0px; padding: 0px; font-size: 16px; font-weight: normal;" class=""></h1><h2 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-7-apply-relevant-changes-to-set" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#7-apply-relevant-changes-to-set" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>7. Apply relevant changes to <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: inherit; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Set</code></h2><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">As the <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Set</code> and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code> types are similar enough to share large chunks of their implementations, it makes sense to look at which of these <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code> enhancements can also be applied to <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Set</code>. Of the symbols proposed above, the following additions would also be useful and appropriate for the <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Set</code> type:</p><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class=""><li style="box-sizing: border-box;" class="">Add a <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Set</code>-specific <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">filter</code> method that returns a new set—this would function essentially as a predicate-based <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">intersection</code> method.</li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Add a <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">capacity</code> property and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">reserveCapacity()</code> method, for the reasons listed above.</li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Modify <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">remove(at:)</code> to return the index of the next entry, likewise.</li></ul></h1><h2 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-detailed-design" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#detailed-design" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>Detailed design</h2><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">With the exception of the proposed capacity property and method, the proposed additions to <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code>, <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Set</code>, and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Sequence</code> are available in <a href="http://swift.sandbox.bluemix.net/#/repl/58daf2d4ecbff41fe22d681a" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">this Swift Sandbox</a>. Note that this prototype is not a proposed implementation; rather a way to try out the behavior of the proposed changes.</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; font-size: 16px; font-weight: normal;" class="">Collected in one place, these are the new APIs for <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code>, <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Set</code>, and <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Sequence</code>:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; font-size: 16px; font-weight: normal;"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">struct</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">Dictionary</span><<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Key</span>: <span class="pl-e" style="box-sizing: border-box; color: rgb(121, 93, 163);"><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Hashable</span></span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">typealias</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">Element</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> (key: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Key</span>, value: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>)
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> existing declarations</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> Creates a new dictionary using the key/value pairs in the given sequence.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> If the given sequence has any duplicate keys, the result is `nil`.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init?</span><<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">S</span>: <span class="pl-e" style="box-sizing: border-box; color: rgb(121, 93, 163);"><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Sequence</span></span>>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">keysAndValues</span>: S) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">where</span> S.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Iterator</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">==</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> Creates a new dictionary using the key/value pairs in the given sequence,</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> using a combining closure to determine the value for any duplicate keys.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span><<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">S</span>: <span class="pl-e" style="box-sizing: border-box; color: rgb(121, 93, 163);"><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Sequence</span></span>>(
<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">merging</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">keysAndValues</span>: S,
<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">resolvingCollisionsWith</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">combine</span>: (<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">throws</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>
) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">rethrows</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">where</span> S.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Iterator</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">==</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> Merges the key/value pairs in the given sequence into the dictionary,</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> using a combining closure to determine the value for any duplicate keys.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">mutating</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">merge</span><<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">S</span>: <span class="pl-e" style="box-sizing: border-box; color: rgb(121, 93, 163);"><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Sequence</span></span>>(
<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">contentsOf</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">other</span>: S,
<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">resolvingCollisionsWith</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">combine</span>: (<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">throws</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>
) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">rethrows</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">where</span> S.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Iterator</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">==</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> Returns a new dictionary created by merging the key/value pairs in the </span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> given sequence into the dictionary, using a combining closure to determine </span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> the value for any duplicate keys.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">merged</span><<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">S</span>: <span class="pl-e" style="box-sizing: border-box; color: rgb(121, 93, 163);"><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Sequence</span></span>>(
<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">with</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">other</span>: S,
<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">resolvingCollisionsWith</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">combine</span>: (<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">throws</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>
) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">rethrows</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> [<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Key</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">where</span> S.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Iterator</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">==</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> Accesses the element with the given key, or the specified default value, </span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> if the dictionary doesn't contain the given key.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">subscript</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">key</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Key</span>, <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">default</span> defaultValue<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span> { <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">get</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">set</span> }
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> Returns a new dictionary containing the key/value pairs that satisfy </span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> the given predicate. </span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">filter</span>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">isIncluded</span>: (<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Key</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">throws</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Bool</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">rethrows</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> [<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Key</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>]
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> Returns a new dictionary containing the existing keys and the results of </span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> mapping the given closure over the dictionary's values.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">mapValues</span><<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">T</span>>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">transform</span>: (<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">throws</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> T) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">rethrows</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> [<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Key</span>: T]
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> The number of key/value pairs that can be stored by the dictionary without</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> reallocating storage.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> capacity<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span> { <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">get</span> }
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> Ensures that the dictionary has enough storage for `capacity` key/value </span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> pairs.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">reserveCapacity</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">_</span> capacity<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>)
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> Removes the key/value pair at the specified index.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">///</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> If you use `remove(at:)` while iterating through the contents of a </span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> dictionary, continue iterating using the index returned as `nextIndex`. </span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> Calling this method invalidates all other previously existing indices.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">///</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> - Returns: A tuple containing the removed key/value pair and the index</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> of the next pair in the dictionary.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">@discardableResult</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">mutating</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">remove</span>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">at</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">index</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Index</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span>
(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">removed</span>: (<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">key</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Key</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">value</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Value</span>), <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">nextIndex</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Index</span>)
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">extension</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);"><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Sequence</span></span> {
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> Returns a dictionary where the keys are the groupings returned by </span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> the given closure and the values are arrays of the elements that </span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> returned each specific key.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">grouped</span><<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Key</span>: <span class="pl-e" style="box-sizing: border-box; color: rgb(121, 93, 163);"><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Hashable</span></span>>(
<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">by</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">grouping</span>: (<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Iterator</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">throws</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Key</span>
) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">rethrows</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> [<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Key</span>: [<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Iterator</span>.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span>]]
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">struct</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">Set</span><<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span>: <span class="pl-e" style="box-sizing: border-box; color: rgb(121, 93, 163);"><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Hashable</span></span>> {
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">//</span> existing declarations</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> Returns a new set containing the elements that satisfy the given predicate.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">filter</span>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">isIncluded</span>: (<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">throws</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Bool</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">rethrows</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Set</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> The number of elements that can be stored by the set without </span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> reallocating storage.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> capacity<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span> { <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">get</span> }
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> Ensures that the set has enough storage for `capacity` elements.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">reserveCapacity</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">_</span> capacity<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>)
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> Removes the element at the specified index.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">///</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> If you use `remove(at:)` while iterating through the contents of a </span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> set, continue iterating using the index returned as `nextIndex`. </span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> Calling this method invalidates all other previously existing indices.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">///</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> - Returns: A tuple containing the removed element and the index</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> of the next element in the set.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">@discardableResult</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">mutating</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">remove</span>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">at</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">index</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Index</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> (removed: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Element</span>, nextIndex: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Index</span>)
}
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> Returns its first argument.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">first</span><<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">T</span>>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">a</span>: T, <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">b</span>: T) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> T
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"><span class="pl-c" style="box-sizing: border-box;">///</span> Returns its last argument.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);"></span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">last</span><<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">T</span>>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">a</span>: T, <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box; color: rgb(51, 51, 51);">b</span>: T) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> T</pre></div></h1><h2 style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-source-compatibility" class="anchor" href="https://gist.github.com/natecook1000/4bd8f20736eb99ed3c5a4cdcc41e9a5f#source-compatibility" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none; float: left; padding-right: 4px; margin-left: -20px; line-height: 1;"></a>Source compatibility</h2><h1 style="box-sizing: border-box; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(234, 236, 239); color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class=""><div style="box-sizing: border-box; margin-top: 0px; font-size: 16px; font-weight: normal; margin-bottom: 0px !important;" class="">A significant majority of the proposed additions are purely additive and should impose no source compatibility burden. The modified return return type for the two <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(27, 31, 35, 0.0470588); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">remove(at:)</code> methods, while additive in nature, will break source compatibility in the cases where the removed value is captured. In theory, a fix-it should be possible that would help in these cases.</div></h1></div></div></div></div></div></div></div></div></body></html>