<div dir="ltr">What's the status of Recursive protocol constraints? it's a feature that will help the design of a library I'm working on.<div>How can I help ?<br><br><div class="gmail_quote"><div dir="ltr">On Tue, Feb 14, 2017 at 1:32 AM Douglas Gregor via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class="gmail_msg"><br class="gmail_msg"><div class="gmail_msg"><blockquote type="cite" class="gmail_msg"><div class="gmail_msg">On Feb 13, 2017, at 1:42 PM, Charles Srstka via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a>> wrote:</div><br class="m_866077578325317742Apple-interchange-newline gmail_msg"><div class="gmail_msg"><div style="word-wrap:break-word" class="gmail_msg"><div class="gmail_msg">The following comment accompanies the declaration of the SubSequence associated type in the Collection protocol:</div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg"><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(0,132,0)" class="gmail_msg"><span style="font-variant-ligatures:no-common-ligatures" class="gmail_msg">/// A sequence that represents a contiguous subrange of the collection's</span></div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(0,132,0)" class="gmail_msg"><span style="font-variant-ligatures:no-common-ligatures" class="gmail_msg">/// elements.</span></div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo" class="gmail_msg"><span style="font-variant-ligatures:no-common-ligatures;color:#008400" class="gmail_msg">///</span></div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(0,132,0)" class="gmail_msg"><span style="font-variant-ligatures:no-common-ligatures" class="gmail_msg">/// This associated type appears as a requirement in the `Sequence`</span></div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(0,132,0)" class="gmail_msg"><span style="font-variant-ligatures:no-common-ligatures" class="gmail_msg">/// protocol, but it is restated here with stricter constraints. In a</span></div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(0,132,0)" class="gmail_msg"><span style="font-variant-ligatures:no-common-ligatures" class="gmail_msg">/// collection, the subsequence should also conform to `Collection`.</span></div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(112,61,170)" class="gmail_msg"><span style="font-variant-ligatures:no-common-ligatures;color:#ba2da2" class="gmail_msg">associatedtype</span><span style="font-variant-ligatures:no-common-ligatures" class="gmail_msg"> SubSequence : </span><span style="font-variant-ligatures:no-common-ligatures" class="gmail_msg">IndexableBase</span><span style="font-variant-ligatures:no-common-ligatures" class="gmail_msg">, </span><span style="font-variant-ligatures:no-common-ligatures" class="gmail_msg">Sequence</span><span style="font-variant-ligatures:no-common-ligatures" class="gmail_msg"> = </span><span style="font-variant-ligatures:no-common-ligatures" class="gmail_msg">Slice</span><span style="font-variant-ligatures:no-common-ligatures" class="gmail_msg"><</span><span style="font-variant-ligatures:no-common-ligatures" class="gmail_msg">Self</span><span style="font-variant-ligatures:no-common-ligatures" class="gmail_msg">></span></div></div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(112,61,170)" class="gmail_msg"><span style="font-variant-ligatures:no-common-ligatures" class="gmail_msg"><br class="gmail_msg"></span></div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(112,61,170)" class="gmail_msg"><span style="font-variant-ligatures:no-common-ligatures" class="gmail_msg"><span style="font-family:Helvetica;font-size:12px" class="gmail_msg">The comments clearly state that the subsequence should conform to Collection, however, it is not declared as such. Why is this?</span></span></div></div></div></blockquote><br class="gmail_msg"></div></div><div style="word-wrap:break-word" class="gmail_msg"><div class="gmail_msg">The compiler doesn’t support “recursive” constraints. We’re working on it</div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg"><span class="m_866077578325317742Apple-tab-span gmail_msg" style="white-space:pre-wrap"> </span><a href="https://gist.github.com/DougGregor/e7c4e7bb4465d6f5fa2b59be72dbdba6" class="gmail_msg" target="_blank">https://gist.github.com/DougGregor/e7c4e7bb4465d6f5fa2b59be72dbdba6</a></div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg"><span class="m_866077578325317742Apple-tab-span gmail_msg" style="white-space:pre-wrap"> </span>- Doug</div><div class="gmail_msg"><br class="gmail_msg"></div><br class="gmail_msg"></div>_______________________________________________<br class="gmail_msg">
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