<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">I'm not attached to the name filteredMap, but having a specific signature for the optional version makes sense. <div class=""><br class=""></div><div class="">I think the problem is that while Optional can be contemplated as a sequence of zero or one items, implicit conversion to Optional means anything can then be interpreted as a collection of one item.<div class=""><br class=""></div><div class="">Likewise, if the syntax for passing in closures required any argument label to be specified, it might be clearer for optional vs sequence, but they are not required.</div><div class=""><br class=""></div><div class="">-DW</div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Oct 23, 2017, at 4:15 PM, Max Moiseev via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html; charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Hi swift-evolution!<div class=""><br class=""></div><div class="">I would like to propose the following change to the standard library:</div><div class=""><br class=""></div><div class="">deprecate `Sequence.flatMap<U>(_: (Element) -> U?) -> [U]` and make this functionality available under a new name `Sequence.filteredMap(_:)`.</div><div class=""><br class=""></div><div class="">The draft is available at <a href="https://gist.github.com/moiseev/2f36376c8ef4c2b1273cff0bfd9c3b95" class="">https://gist.github.com/moiseev/2f36376c8ef4c2b1273cff0bfd9c3b95</a> and is included below for your convenience.</div><div class=""><br class=""></div><div class="">Max</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="">Introduce Sequence.filteredMap(_:)</h1><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);" class=""><li style="box-sizing: border-box;" class="">Proposal: <a href="https://gist.github.com/moiseev/NNNN-filename.md" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">SE-NNNN</a></li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Authors: <a href="https://github.com/moiseev" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(3, 102, 214); text-decoration: none;" class="">Max Moiseev</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 implementation</span></li></ul><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 href="https://gist.github.com/moiseev/2f36376c8ef4c2b1273cff0bfd9c3b95#introduction" aria-hidden="true" class="anchor" id="user-content-introduction" 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;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Introduction</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);" class="">We propose to deprecate the controversial version 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="">Sequence.flatMap</code> method and provide the same functionality under a different, and potentially more descriptive, name.</p><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 href="https://gist.github.com/moiseev/2f36376c8ef4c2b1273cff0bfd9c3b95#motivation" aria-hidden="true" class="anchor" id="user-content-motivation" 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;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Motivation</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);" class="">The Swift standard library currently defines 3 distinct overloads 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="">flatMap</code>:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);"><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; word-wrap: normal; padding: 16px; overflow: auto; line-height: 1.45; 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-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">Sequence</span>.<span class="pl-smi" style="box-sizing: border-box;">flatMap</span><span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);"><</span>S<span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">></span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">_</span>: (<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">Element</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">-></span> S) <span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">-></span> [S.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">Element</span>]
<span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">where</span> S <span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">Sequence</span>
<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">Optional</span>.<span class="pl-smi" style="box-sizing: border-box;">flatMap</span><span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);"><</span>U<span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">></span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">_</span>: (Wrapped) <span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">-></span> U<span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">?</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">-></span> U<span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">?</span>
<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">Sequence</span>.<span class="pl-smi" style="box-sizing: border-box;">flatMap</span><span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);"><</span>U<span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">></span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">_</span>: (<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">Element</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">-></span> U<span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">?</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">-></span> [U]</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);" class="">The last one, despite being useful in certain situations, can be (and often is) misused. Consider the following snippet:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);"><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; word-wrap: normal; padding: 16px; overflow: auto; line-height: 1.45; 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(215, 58, 73);">struct</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(111, 66, 193);">Person</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">var</span> age<span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">Int</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">var</span> name<span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">String</span>
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(111, 66, 193);">getAges</span>(<span class="pl-smi" style="box-sizing: border-box;"><span class="pl-en" style="box-sizing: border-box; color: rgb(111, 66, 193);">people</span></span>: [Person]) <span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">-></span> [<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">Int</span>] {
<span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">return</span> people.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">flatMap</span> { <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">$0</span>.<span class="pl-smi" style="box-sizing: border-box;">age</span> }
}</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);" class="">What happens inside <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="">getNames</code> is: thanks to the implicit promotion 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="">Optional</code>, the result of the closure gets wrapped into 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="">.some</code>, then immediately unwrapped by the implementation 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="">flatMap</code>, and appended to the result array. All this unnecessary wrapping and unwrapping can be easily avoided by just using <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> instead.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);"><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; word-wrap: normal; padding: 16px; overflow: auto; line-height: 1.45; 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(215, 58, 73);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(111, 66, 193);">getAges</span>(<span class="pl-smi" style="box-sizing: border-box;"><span class="pl-en" style="box-sizing: border-box; color: rgb(111, 66, 193);">people</span></span>: [Person]) <span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">-></span> [<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">Int</span>] {
<span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">return</span> people.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">map</span> { <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">$0</span>.<span class="pl-smi" style="box-sizing: border-box;">age</span> }
}</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);" class="">It gets even worse when we consider future code modifications, like the one where Swift 4 introduced 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="">String</code>conformance to 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="">Collection</code> protocol. The following code used to compile (due to 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="">flatMap</code> overload in question).</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);"><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; word-wrap: normal; padding: 16px; overflow: auto; line-height: 1.45; 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(215, 58, 73);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(111, 66, 193);">getNames</span>(<span class="pl-smi" style="box-sizing: border-box;"><span class="pl-en" style="box-sizing: border-box; color: rgb(111, 66, 193);">people</span></span>: [Person]) <span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">-></span> [<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">String</span>] {
<span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">return</span> people.<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">flatMap</span> { <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">$0</span>.<span class="pl-smi" style="box-sizing: border-box;">name</span> }
}</pre></div><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);" class="">But it no longer does, because now there is a better overload that does not involve implicit promotion. In this particular case, the compiler error would be obvious, as it would point at the same line where <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="">flatMap</code> is used. Imagine however if it was just 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="">let names = people.flatMap { $0.name }</code> statement, and 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="">names</code> variable were used elsewhere. The compiler error would be misleading.</p><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 href="https://gist.github.com/moiseev/2f36376c8ef4c2b1273cff0bfd9c3b95#proposed-solution" aria-hidden="true" class="anchor" id="user-content-proposed-solution" 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;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Proposed solution</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);" class="">We propose to deprecate the controversial overload 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="">flatMap</code> and re-introduce the same functionality under a new name. The name being <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="">filteredMap(_:)</code> as we believe it best describes the intent of this function.</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);" class="">For reference, here are the alternative names from other languages:</p><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);" class=""><li style="box-sizing: border-box;" class="">Haskell, Idris <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="">
mapMaybe :: (a -> Maybe b) -> [a] -> [b]</code></li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Ocaml (Core and Batteries)
<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_map : 'a t -> f:('a -> 'b option) -> 'b t</code></li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">F#
<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="">List.choose : ('T -> 'U option) -> 'T list -> 'U list</code></li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Rust
<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="">fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F>
where F: FnMut(Self::Item) -> Option<B></code></li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Scala <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="">
def collect[B](pf: PartialFunction[A, B]): List[B]</code></li></ul><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 href="https://gist.github.com/moiseev/2f36376c8ef4c2b1273cff0bfd9c3b95#source-compatibility" aria-hidden="true" class="anchor" id="user-content-source-compatibility" 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;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Source compatibility</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);" class="">Since the old function will still be available (although deprecated) all the existing code will compile, producing a deprecation warning and a fix-it.</p><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 href="https://gist.github.com/moiseev/2f36376c8ef4c2b1273cff0bfd9c3b95#effect-on-abi-stability" aria-hidden="true" class="anchor" id="user-content-effect-on-abi-stability" 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;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Effect on ABI stability</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);" class="">This is an additive API change, and does not affect ABI stability.</p><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 href="https://gist.github.com/moiseev/2f36376c8ef4c2b1273cff0bfd9c3b95#effect-on-api-resilience" aria-hidden="true" class="anchor" id="user-content-effect-on-api-resilience" 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;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Effect on API resilience</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);" class="">Ideally, the deprecated <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="">flatMap</code> overload would not exist at the time when ABI stability is declared, but in the worst case, it will be available in a deprecated form from a library post-ABI stability.</p><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 href="https://gist.github.com/moiseev/2f36376c8ef4c2b1273cff0bfd9c3b95#alternatives-considered" aria-hidden="true" class="anchor" id="user-content-alternatives-considered" 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;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Alternatives considered</h2><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);" class="">It was attempted in the past to warn about this kind of misuse and do the right thing instead by means of a deprecated overload with a non-optional-returning closure. The attempt failed due to another implicit promotion (this time 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="">Any</code>).</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; 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"; font-size: 16px; background-color: rgb(255, 255, 255);" class="">The following alternative names for this function were considered:</p><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; 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"; font-size: 16px; background-color: rgb(255, 255, 255); margin-bottom: 0px !important;" class=""><li style="box-sizing: border-box;" 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="">mapNonNil(_:)
</code> Does not communicate what happens to nil’s</li><li style="box-sizing: border-box; margin-top: 0.25em;" 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="">mapSome(_:)
</code> Reads more like «map some elements of the sequence, but not the others» rather than «process only the ones that produce an Optional.some»</li><li style="box-sizing: border-box; margin-top: 0.25em;" 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="">filterMap(_:)</code>
Does not really follow the naming guidelines and doesn’t seem to be common enough to be considered a term of art.</li></ul><div class=""><br class=""></div></div></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class="">https://lists.swift.org/mailman/listinfo/swift-evolution<br class=""></div></blockquote></div><br class=""></div></div></body></html>