<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=""><br class=""><div><blockquote type="cite" class=""><div class="">On Aug 2, 2017, at 6:49 PM, Rock Yang <<a href="mailto:rockyang@icloud.com" class="">rockyang@icloud.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class=""><div class="">I found maybe it's unable to provide implementation in protocol declaration which has associatedtype.</div><div class=""><br data-mce-bogus="1" class=""></div><div class="">Here is Sequence, which has Subsequence as associatedtype. AnySequence is inferred if no custom Subsequence is declared.</div><div class=""><br data-mce-bogus="1" class=""></div><div class=""><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(255, 255, 255); background-color: rgb(0, 0, 0);" class=""><span style="color: #de38a5;" data-mce-style="color: #de38a5;" class="">extension</span> <span style="color: #00b1ff;" data-mce-style="color: #00b1ff;" class="">Sequence</span> <span style="color: #de38a5;" data-mce-style="color: #de38a5;" class="">where</span> <span style="color: #de38a5;" data-mce-style="color: #de38a5;" class="">Self</span>.Element == <span style="color: #de38a5;" data-mce-style="color: #de38a5;" class="">Self</span>.SubSequence.Element, <span style="color: #de38a5;" data-mce-style="color: #de38a5;" class="">Self</span>.SubSequence : <span style="color: #00b1ff;" data-mce-style="color: #00b1ff;" class="">Sequence</span>, <span style="color: #de38a5;" data-mce-style="color: #de38a5;" class="">Self</span>.SubSequence == <span style="color: #de38a5;" data-mce-style="color: #de38a5;" class="">Self</span>.SubSequence.SubSequence {</div><div style="margin: 0px; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Helvetica; background-color: rgb(0, 0, 0); min-height: 14px;" class=""><br class=""></div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(75, 209, 86); background-color: rgb(0, 0, 0);" class=""><span style="color: #ffffff;" data-mce-style="color: #ffffff;" class=""> </span>/// Returns a subsequence containing all but the given number of initial</div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(75, 209, 86); background-color: rgb(0, 0, 0);" class=""><span style="color: #ffffff;" data-mce-style="color: #ffffff;" class=""> </span>/// elements.</div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(255, 255, 255); background-color: rgb(0, 0, 0);" class=""> <span style="color: #4bd156;" data-mce-style="color: #4bd156;" class="">///</span></div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(75, 209, 86); background-color: rgb(0, 0, 0);" class=""><span style="color: #ffffff;" data-mce-style="color: #ffffff;" class=""> </span>/// If the number of elements to drop exceeds the number of elements in</div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(75, 209, 86); background-color: rgb(0, 0, 0);" class=""><span style="color: #ffffff;" data-mce-style="color: #ffffff;" class=""> </span>/// the sequence, the result is an empty subsequence.</div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(255, 255, 255); background-color: rgb(0, 0, 0);" class=""> <span style="color: #4bd156;" data-mce-style="color: #4bd156;" class="">///</span></div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(75, 209, 86); background-color: rgb(0, 0, 0);" class=""><span style="color: #ffffff;" data-mce-style="color: #ffffff;" class=""> </span>/// let numbers = [1, 2, 3, 4, 5]</div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(75, 209, 86); background-color: rgb(0, 0, 0);" class=""><span style="color: #ffffff;" data-mce-style="color: #ffffff;" class=""> </span>/// print(numbers.dropFirst(2))</div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(75, 209, 86); background-color: rgb(0, 0, 0);" class=""><span style="color: #ffffff;" data-mce-style="color: #ffffff;" class=""> </span>/// // Prints "[3, 4, 5]"</div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(75, 209, 86); background-color: rgb(0, 0, 0);" class=""><span style="color: #ffffff;" data-mce-style="color: #ffffff;" class=""> </span>/// print(numbers.dropFirst(10))</div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(75, 209, 86); background-color: rgb(0, 0, 0);" class=""><span style="color: #ffffff;" data-mce-style="color: #ffffff;" class=""> </span>/// // Prints "[]"</div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(255, 255, 255); background-color: rgb(0, 0, 0);" class=""> <span style="color: #4bd156;" data-mce-style="color: #4bd156;" class="">///</span></div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(75, 209, 86); background-color: rgb(0, 0, 0);" class=""><span style="color: #ffffff;" data-mce-style="color: #ffffff;" class=""> </span>/// - Parameter n: The number of elements to drop from the beginning of</div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(75, 209, 86); background-color: rgb(0, 0, 0);" class=""><span style="color: #ffffff;" data-mce-style="color: #ffffff;" class=""> </span>/// the sequence. `n` must be greater than or equal to zero.</div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(75, 209, 86); background-color: rgb(0, 0, 0);" class=""><span style="color: #ffffff;" data-mce-style="color: #ffffff;" class=""> </span>/// - Returns: A subsequence starting after the specified number of</div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(75, 209, 86); background-color: rgb(0, 0, 0);" class=""><span style="color: #ffffff;" data-mce-style="color: #ffffff;" class=""> </span>/// elements.</div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(255, 255, 255); background-color: rgb(0, 0, 0);" class=""> <span style="color: #4bd156;" data-mce-style="color: #4bd156;" class="">///</span></div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(75, 209, 86); background-color: rgb(0, 0, 0);" class=""><span style="color: #ffffff;" data-mce-style="color: #ffffff;" class=""> </span>/// - Complexity: O(1).</div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Helvetica; color: rgb(255, 255, 255); background-color: rgb(0, 0, 0);" class=""> <span style="color: #de38a5;" data-mce-style="color: #de38a5;" class="">public</span> <span style="color: #de38a5;" data-mce-style="color: #de38a5;" class="">func</span> dropFirst(<span style="color: #de38a5;" data-mce-style="color: #de38a5;" class="">_</span> n: <span style="color: #00b1ff;" data-mce-style="color: #00b1ff;" class="">Int</span>) -> <span style="color: #00b1ff;" data-mce-style="color: #00b1ff;" class="">AnySequence</span><<span style="color: #00b1ff;" data-mce-style="color: #00b1ff;" class="">Self</span>.<span style="color: #00b1ff;" data-mce-style="color: #00b1ff;" class="">Element</span>></div></div><div class=""><br class=""></div><div class="">I think it happened here. It's impossible to put this implementation in the procotol body, even without the constraints. Compiler would never know, dropFirst returns an AnySequence or associatetype Subsequence.</div><div class=""><br data-mce-bogus="1" class=""></div></div></div></blockquote><div><br class=""></div><div>This is a bit different. The implementation is provided in a constrained extension. Depending on the exact type that conforms to Sequence, it may or may not be implemented.</div><div>Even so, that's unrelated to my original proposal.</div><br class=""><blockquote type="cite" class=""><div class=""><div class=""><div class=""><br class="">2017年8月2日 下午11:27，Gor Gyolchanyan via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> 写道：<br class=""><br class=""></div><div class=""><blockquote type="cite" class=""><div class="msg-quote" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" data-mce-style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Aug 2, 2017, at 6:15 PM, Taylor Swift <<a href="mailto:kelvin13ma@gmail.com" class="" data-mce-href="mailto:kelvin13ma@gmail.com">kelvin13ma@gmail.com</a>> wrote:</div><div class=""><div dir="ltr" class=""><div class=""><div class="">I agree with this, extensions on types defined in the same file are generally silly, and default implementations belong in the protocol body. I don’t agree with certain style guides prescription of same-file extensions; they should only be used to hide protocol conformances that are “unimportant” to the functionality of the type. In practice this means only conformances like <span style="font-family: monospace,monospace;" class="" data-mce-style="font-family: monospace,monospace;">CustomStringConvertible</span> and <span style="font-family: monospace,monospace;" class="" data-mce-style="font-family: monospace,monospace;">CustomDebugStringConvertible</span> live in extensions.<br class=""><br class=""></div>If you want to group related methods, use linebreaks and whitespace for that. Don’t split up the type braces since that messes up the whole one-set-of-braces == one type definition visual rule.<br class=""><br class=""></div>The only time it ever makes sense to extend a non concrete type that you own is when adding conditional default implementations. Having to extend a bare protocol is the product of a language limitation.</div></div></blockquote><div class=""><br class=""></div><div class="">Take a look at my replies to Tino Heth about code locality and the rest...</div><br class=""><blockquote type="cite" class=""><div class=""><div class="gmail_extra"><div class="gmail_quote">On Wed, Aug 2, 2017 at 6:26 AM, Tino Heth via swift-evolution <span dir="ltr" class=""><<a href="mailto:swift-evolution@swift.org" class="" data-mce-href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin: 0 0 0 .8ex; border-left: 1px #ccc solid; padding-left: 1ex;" data-mce-style="margin: 0 0 0 .8ex; border-left: 1px #ccc solid; padding-left: 1ex;"><div style="word-wrap: break-word;" class="" data-mce-style="word-wrap: break-word;"><div class=""><span class=""><br class=""><blockquote type="cite" class=""><div class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; float: none; display: inline!important;" class="" data-mce-style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; float: none; display: inline!important;">That would work as well, but it has the downside of forcing a potentially huge number of methods to be implemented in a single place, reducing the readability as opposed to packing them into semantically related groups in the form of extensions.</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="" data-mce-style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"></div></blockquote></span><div class="">I really don't get why people are so obsessed with same-file extensions:<div class="">They are recommended in style guides, influencers blog about them, and they motivated a ridiculous complex change in the access rights system. Yet I haven't seen any evidence that they offer real benefit.</div><div class="">Extensions are great for adding useful helpers to existing types, and still allow you to selectively expose details of your own classes — but most people seem to ignore those options and focus on something can be done better with plain old comments.</div><div class="">[sorry for the rant — but I think a critical look at extensions is long overdue: I rarely see someone questioning their role, so basically, we are making important decisions based on pure superstition]</div><div class=""><br class=""></div><div class="">A protocol itself is already a vehicle to group related methods, and if you have a huge entity, it doesn't get better just because you split it and hide its complexity.</div></div><span class=""><br class=""><blockquote type="cite" class=""><div class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; float: none; display: inline!important;" class="" data-mce-style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; float: none; display: inline!important;">Also, please include the original message for reference purposes.</span></div></blockquote></span></div>[hopes Discourse will happen soon ;-) ]</div><br class="">______________________________<wbr class="">_________________<br class=""> swift-evolution mailing list<br class=""> <a href="mailto:swift-evolution@swift.org" class="" data-mce-href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br class=""> <a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" class="" data-mce-href="https://lists.swift.org/mailman/listinfo/swift-evolution">https://lists.swift.org/<wbr class="">mailman/listinfo/swift-<wbr class="">evolution</a><br class=""> <br class=""></blockquote></div><br class=""></div></div></blockquote></div><br class=""><div class="_stretch"><span class="body-text-content">_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" data-mce-href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" data-mce-href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class=""></span></div></div></blockquote></div></div></div></blockquote></div><br class=""></body></html>