<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 Jan 13, 2017, at 2:30 PM, David Sweeris 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 dir="auto" class=""><div class=""><br class=""></div><div class="">On Jan 13, 2017, at 15:10, Anton Zhilin via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""></div><blockquote type="cite" class=""><div dir="ltr" class=""><div class="markdown-here-wrapper" style=""><p style="margin:0px 0px 1.2em!important" class="">That seems pretty close to Rust’s <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline" class="">derive</code>. Why not invent a similar syntax in Swift? Otherwise it will make us look through all the sources to make sure deriving is used.</p>
<pre style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;font-size:1em;line-height:1.2em;margin:1.2em 0px" class=""><code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline;white-space:pre;overflow:auto;border-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important" class="">enum Option: @derive Equatable {
...
}
</code></pre><p style="margin:0px 0px 1.2em!important" class="">Also, we can get better looking compilation errors, like:</p>
<pre style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;font-size:1em;line-height:1.2em;margin:1.2em 0px" class=""><code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline;white-space:pre;overflow:auto;border-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important" class="">ERROR at line 1, col 14: could not derive Equatable for Option
enum Option: @derive Equatable {
^~~~~~~~~~~~~~~~~</code></pre></div></div></blockquote><br class=""><div class="">I think that idea came up once before... can't remember where, though, or what we thought of it at the time.</div><div class=""><br class=""></div><div class="">As far as reducing enum boilerplate, what about borrowing the generic system's syntax and looking at it from the switch's PoV?</div><div class="">func == (lhs: MyEnum, r<span style="background-color: rgba(255, 255, 255, 0);" class="">hs: MyEnum) -> Bool {</span></div><div class=""> switch <c is MyEnum> (lhs, rhs) {</div><div class=""> case (c(let lVal), c(let rVal)): // both lhs and rhs are "c" and the same case</div><div class=""> return lVal == rVal //syntax error if `==` isn't defined for the associated value types of every case</div><div class=""> default: return false</div><div class=""> }</div><div class="">}</div></div></div></blockquote><div><br class=""></div>I think initially, we would like to implement deriving these witnesses directly in the compiler, instead of trying to come up with a metaprogramming syntax for them.</div><div><br class=""></div><div>Slava</div><div><br class=""><blockquote type="cite" class=""><div class=""><div dir="auto" class=""><div class=""><br class=""></div><div class="">- Dave Sweeris</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=""></body></html>