<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=""><div><blockquote type="cite" class=""><div class="">On Feb 19, 2017, at 6:13 PM, Ben Cohen 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=""><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><blockquote type="cite" class=""><div class="">On Feb 19, 2017, at 11:22 AM, Ole Begemann <<a href="mailto:ole@oleb.net" class="">ole@oleb.net</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><blockquote type="cite" class=""><div class="">On 17 Feb 2017, at 01:26, Ben Cohen 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=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><p class="" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255); margin-top: 0px !important;">Here is a list of commonly requested changes/enhancements to <code class="" style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">Dictionary</code>, all of which would probably be appropriate to put together into a single evolution proposal:</p><ul class="" style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255);"><li class="" style="box-sizing: border-box;"><code class="" style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">init</code> from/<code class="" style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">merge</code> in a <code class="" style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">Sequence</code> of <code class="" style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">Key/Value</code> pairs (already raised as SE-100: <a href="https://github.com/apple/swift-evolution/blob/master/proposals/0100-add-sequence-based-init-and-merge-to-dictionary.md" class="" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none;">https://github.com/apple/swift-evolution/blob/master/proposals/0100-add-sequence-based-init-and-merge-to-dictionary.md</a>).</li><li class="" style="box-sizing: border-box; margin-top: 0.25em;">make the <code class="" style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">Values</code> view collection a <code class="" style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">MutableCollection</code> (as in this PR: <a href="https://github.com/apple/swift-evolution/pull/555" class="" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none;">https://github.com/apple/swift-evolution/pull/555</a>).</li><li class="" style="box-sizing: border-box; margin-top: 0.25em;">Add a defaulting <code class="" style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">subscript</code> <code class="" style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">get</code> (e.g. <code class="" style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">counts[key, default: 0] += 1</code> or <code class="" style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">grouped(key, default:[]].append(value)</code>).</li><li class="" style="box-sizing: border-box; margin-top: 0.25em;">Add a group by-like init to create a <code class="" style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">Dictionary<K,[V]></code> from a sequence of <code class="" style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">V</code> and a closure <code class="" style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">(V)->K</code>.</li></ul></div></div></blockquote><div class="">Out of interest, how would you implement this? Does it require a generics feature that's slated for Swift 4? I tried two approaches that don't compile in a current Swift 3.1 snapshot (and I'm getting a segfault with both examples in a dev snapshot from 2017-02-14):</div><div class=""><br class=""></div><div class="">1)</div><div class=""><br class=""></div><div class=""><div class="" style="margin: 0px; line-height: normal; font-family: Menlo;"><span class="" style="color: rgb(196, 34, 117); font-variant-ligatures: no-common-ligatures;">extension</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">Dictionary</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span></div><div class="" style="margin: 0px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> </span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(138, 138, 138);">// error: same-type constraint 'Value' == '[S.Iterator.Element]' is recursive</span></div><div class="" style="margin: 0px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> </span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(196, 34, 117);">init</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><S:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(97, 34, 174);">Sequence</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>(values:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(83, 154, 164);">S</span><span class="" style="font-variant-ligatures: no-common-ligatures;">, groupedBy: (</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(83, 154, 164);">S</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.Iterator.Element) -><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">Key</span><span class="" style="font-variant-ligatures: no-common-ligatures;">)</span></div><div class="" style="margin: 0px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> </span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(196, 34, 117);">where</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">Value</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>== [</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(83, 154, 164);">S</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.Iterator.Element] {</span></div><div class="" style="margin: 0px; line-height: normal; font-family: Menlo;"> ...</div><div class="" style="margin: 0px; line-height: normal; font-family: Menlo;"> }</div><div class="" style="margin: 0px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> }</span></div><div class="" style="margin: 0px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;">}</span></div><div class=""><span class="" style="font-variant-ligatures: no-common-ligatures;"><br class=""></span></div><div class="">2)</div></div></div><div class=""><br class=""></div><div class=""><div class="" style="margin: 0px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(138, 138, 138);">// error: reference to generic type 'Array' requires arguments in <...></span></div><div class="" style="margin: 0px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(196, 34, 117);">extension</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">Dictionary</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(196, 34, 117);">where</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>Value == Array {</span></div><div class="" style="margin: 0px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> </span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(196, 34, 117);">init</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><S:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(97, 34, 174);">Sequence</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>(values:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(83, 154, 164);">S</span><span class="" style="font-variant-ligatures: no-common-ligatures;">, groupedBy: (</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(83, 154, 164);">S</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.Iterator.Element) -> Key)</span></div><div class="" style="margin: 0px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> </span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(196, 34, 117);">where</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(83, 154, 164);">S</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.Iterator.Element ==<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(97, 34, 174);">Value</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(97, 34, 174);">Element</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span></div><div class="" style="margin: 0px; line-height: normal; font-family: Menlo;"> ...</div><div class="" style="margin: 0px; line-height: normal; font-family: Menlo;"> }</div><div class="" style="margin: 0px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> }</span></div><div class="" style="margin: 0px; line-height: normal; font-family: Menlo;">}</div></div></div></div></blockquote></div></div></blockquote><div><br class=""></div><div>I don't totally have my head around this, but won't a Dictionary initializer like this require parameterized extensions as described in the generics manifesto? </div><div><span class="Apple-tab-span" style="white-space:pre"> </span><a href="https://github.com/apple/swift/blob/master/docs/GenericsManifesto.md#parameterized-extensions" class="">https://github.com/apple/swift/blob/master/docs/GenericsManifesto.md#parameterized-extensions</a></div><div><br class=""></div><div>Something like this:</div><div><br class=""></div></div><blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class=""><div><div><font face="Menlo" class="">extension Dictionary<T> where Value == [T] {</font></div></div><div><div><font face="Menlo" class=""> init<S: Sequence>(_ values: S, groupedBy: (S.Iterator.Element) -> Key) </font></div><div><font face="Menlo" class=""> where S.Iterator.Element == T </font></div><div><font face="Menlo" class=""> { </font><span style="font-family: Menlo;" class="">...</span><span style="font-family: Menlo;" class=""> }</span></div></div><div><div><font face="Menlo" class="">}</font></div></div></blockquote><div><div><br class=""></div><div>For what it's worth, I had been expecting that we'd add this as a method on Sequence, a la joined(by:), not an initializer.</div><div><br class=""></div></div><blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class=""><div><div><font face="Menlo" class="">extension Sequence {</font></div></div><div><div><font face="Menlo" class=""> func grouped<Key: Hashable>(by grouping: (Iterator.Element) -> Key) </font></div><div><font face="Menlo" class=""> -> [Key: [Iterator.Element]] </font></div><div><font face="Menlo" class=""> { ... }</font></div></div><div><div><font face="Menlo" class="">}</font></div><div><font face="Menlo" class="">let d = (1...10).grouped(by: { $0 % 3 })</font></div><div><font face="Menlo" class="">// [2: [2, 5, 8], 0: [3, 6, 9], 1: [1, 4, 7, 10]]</font></div></div></blockquote><div><div><br class=""></div><div>Nate</div><div><br class=""></div><blockquote type="cite" class=""><div class=""><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">Oops, looks like a bug in the same-type constraint implementation. Ought to work in 3.1. Minimal crasher repro:</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(4, 51, 255);"><span class="" style="font-variant-ligatures: no-common-ligatures;">extension</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">Array</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(52, 149, 175);"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">func</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>f<S:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures;">Sequence</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>() </span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(52, 149, 175);"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);"> where</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures;">Element</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>==<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures;">S</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures;">Iterator</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures;">Element</span><span class="" style="font-variant-ligatures: no-common-ligatures;">? {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;" class=""><span class="" style="font-variant-ligatures: no-common-ligatures;"> </span><br class="webkit-block-placeholder"></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> } </span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;">}</span></div></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">I’ve raised<span class="Apple-converted-space"> </span><a href="https://bugs.swift.org/browse/SR-4008" class="">https://bugs.swift.org/browse/SR-4008</a></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">It ought to be done with the first one. For the second, you can’t constrain Value == Array because Array isn’t a type, needs to be Array<Something>.</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">As an (impractical) workaround, this compiles:</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(52, 149, 175);"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">extension</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures;">Dictionary</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">subscript</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(k:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">Key</span><span class="" style="font-variant-ligatures: no-common-ligatures;">, default<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">default</span><span class="" style="font-variant-ligatures: no-common-ligatures;">:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">Value</span><span class="" style="font-variant-ligatures: no-common-ligatures;">) -><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">Value</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">get</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">return</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">self</span><span class="" style="font-variant-ligatures: no-common-ligatures;">[k] ?? `default` }</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">set</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">self</span><span class="" style="font-variant-ligatures: no-common-ligatures;">[k] = newValue }</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> }</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;">}</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">extension</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">Dictionary</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">where</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>Value: RangeReplaceableCollection {</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">init</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><S:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">Sequence</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>(grouping values:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">S</span><span class="" style="font-variant-ligatures: no-common-ligatures;">, by: (</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">S</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.Iterator.Element) -><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">Key</span><span class="" style="font-variant-ligatures: no-common-ligatures;">)</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">where</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">S</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.Iterator.Element ==<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">Value</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.Iterator.Element {</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">self</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>= [:]</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">for</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>x<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">in</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>values {</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">let</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>k = by(x)</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">self</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">[</span><span class="" style="font-variant-ligatures: no-common-ligatures;">k, default:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">Value</span><span class="" style="font-variant-ligatures: no-common-ligatures;">()</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">]</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">append</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(x)</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> }</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> }</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;">}</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">let</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>s = [10,20,22,30,31]</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(0, 143, 0);"><span class="" style="font-variant-ligatures: no-common-ligatures;">// have to explicitly type the Dictionary as a specific RRC</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">let</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>d: [</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">Int</span><span class="" style="font-variant-ligatures: no-common-ligatures;">:[</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">Int</span><span class="" style="font-variant-ligatures: no-common-ligatures;">]] =<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">Dictionary</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(grouping:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">s</span><span class="" style="font-variant-ligatures: no-common-ligatures;">) { $0%10 }</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(52, 149, 175);"><span class="" style="font-variant-ligatures: no-common-ligatures;">print</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(</span><span class="" style="font-variant-ligatures: no-common-ligatures;">d</span><span class="" style="font-variant-ligatures: no-common-ligatures;">)</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;"><br class=""><span class="" style="font-variant-ligatures: no-common-ligatures;"></span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span></div></div><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">_______________________________________________</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">swift-evolution mailing list</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><a href="mailto:swift-evolution@swift.org" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">swift-evolution@swift.org</a><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a></div></blockquote></div><br class=""></body></html>