<div dir="ltr">Such a proposed syntax doesn't solve the general problem though, which is that comparing two enum values requires enumerating all of the cases to test whether they are (1) the same and (2) have the same associated values, if any. The desire here is to get rid of the boilerplate that users must write to implement simple equality (and hashability, in the case of my proposal draft), similarly to how enums without associated values already get Equatable and Hashable for free.<div><br></div></div><br><div class="gmail_quote"><div dir="ltr">On Fri, Jan 13, 2017 at 3:37 PM Derrick Ho 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">I think it is better to create a syntax for getting the associated values and then comparing them.<br class="gmail_msg"><br class="gmail_msg">enum Option {<br class="gmail_msg"> case foo(String)<br class="gmail_msg"> case bar(Int)<br class="gmail_msg"> case zip<br class="gmail_msg">}<br class="gmail_msg"><br class="gmail_msg">let op = Option.foo("hello")<br class="gmail_msg">let bb = Option.foo("world")<br class="gmail_msg"><br class="gmail_msg">// proposed tuple-like syntax<br class="gmail_msg"><br class="gmail_msg">op.foo.0 // returns Optional("hello")<br class="gmail_msg"><br class="gmail_msg">// then we can compare values directly<br class="gmail_msg"><br class="gmail_msg">if op.foo.0 == bb.foo.0 {<br class="gmail_msg">// ...<br class="gmail_msg">}<br class="gmail_msg"><br class="gmail_msg"><div class="gmail_quote gmail_msg"><div dir="ltr" class="gmail_msg">On Fri, Jan 13, 2017 at 5:44 PM Slava Pestov via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a>> wrote:<br class="gmail_msg"></div><blockquote class="gmail_quote gmail_msg" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class="gmail_msg"><div class="gmail_msg"><blockquote type="cite" class="gmail_msg"><div class="gmail_msg">On Jan 13, 2017, at 2:30 PM, David Sweeris 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_-109426287205270283m_-5931170447479371561Apple-interchange-newline gmail_msg"><div class="gmail_msg"><div dir="auto" class="gmail_msg"><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">On Jan 13, 2017, at 15:10, Anton Zhilin via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a>> wrote:<br class="gmail_msg"><br class="gmail_msg"></div><blockquote type="cite" class="gmail_msg"><div dir="ltr" class="gmail_msg"><div class="m_-109426287205270283m_-5931170447479371561markdown-here-wrapper gmail_msg"><p style="margin:0px 0px 1.2em!important" class="gmail_msg">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="gmail_msg">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="gmail_msg"><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-wrap;overflow:auto;border-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important" class="gmail_msg">enum Option: @derive Equatable {
...
}
</code></pre><p style="margin:0px 0px 1.2em!important" class="gmail_msg">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="gmail_msg"><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-wrap;overflow:auto;border-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important" class="gmail_msg">ERROR at line 1, col 14: could not derive Equatable for Option
enum Option: @derive Equatable {
^~~~~~~~~~~~~~~~~</code></pre></div></div></blockquote><br class="gmail_msg"><div class="gmail_msg">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="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">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="gmail_msg">func == (lhs: MyEnum, r<span style="background-color:rgba(255,255,255,0)" class="gmail_msg">hs: MyEnum) -> Bool {</span></div><div class="gmail_msg"> switch <c is MyEnum> (lhs, rhs) {</div><div class="gmail_msg"> case (c(let lVal), c(let rVal)): // both lhs and rhs are "c" and the same case</div><div class="gmail_msg"> return lVal == rVal //syntax error if `==` isn't defined for the associated value types of every case</div><div class="gmail_msg"> default: return false</div><div class="gmail_msg"> }</div><div class="gmail_msg">}</div></div></div></blockquote><div class="gmail_msg"><br class="gmail_msg"></div></div></div><div style="word-wrap:break-word" class="gmail_msg"><div class="gmail_msg">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><div style="word-wrap:break-word" class="gmail_msg"><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">Slava</div></div><div style="word-wrap:break-word" class="gmail_msg"><div class="gmail_msg"><br class="gmail_msg"><blockquote type="cite" class="gmail_msg"><div class="gmail_msg"><div dir="auto" class="gmail_msg"><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">- Dave Sweeris</div></div>_______________________________________________<br class="gmail_msg">swift-evolution mailing list<br class="gmail_msg"><a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a><br class="gmail_msg"><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="gmail_msg" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class="gmail_msg"></div></blockquote></div><br class="gmail_msg"></div>_______________________________________________<br class="gmail_msg">
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