<div dir="ltr">This is a request that comes up frequently; I wrote an early draft proposal for it several months ago, with it covering all value types, not just enums, and also including Hashable as well as Equatable:<div><br></div><div><a href="https://gist.github.com/allevato/2fd10290bfa84accfbe977d8ac07daad">https://gist.github.com/allevato/2fd10290bfa84accfbe977d8ac07daad</a><br></div><div><br></div><div>Since it's purely additive, it won't get much attention until phase 2 at the earliest, but I'd like to revisit it then. Most of the discussion before revolved around to what degree users should have to opt-in or opt-out of this functionality.</div><div><br></div><div>Re: generics, I don't think there's anything on the roadmap that goes into such deep detail as "if every associated value of every enum case is Equatable, then X is also Equatable", and I don't think there would be a clean way to express that with the generics syntax. This would probably have to be something that's baked into the compiler to synthesize == and hashValue for types that satisfy the constraints.</div><div><br></div></div><br><div class="gmail_quote"><div dir="ltr">On Fri, Jan 13, 2017 at 12:31 PM David Sweeris 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 dir="auto" class="gmail_msg"><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg"><div class="gmail_msg"><br class="gmail_msg"><br class="gmail_msg">Sent from my iPhone</div></div></div><div dir="auto" class="gmail_msg"><div class="gmail_msg">On Jan 13, 2017, at 13:51, Adam Shin 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></div><div dir="auto" class="gmail_msg"><blockquote type="cite" class="gmail_msg"><div class="gmail_msg"><div dir="ltr" class="gmail_msg"><div class="gmail_msg" style="font-size:13px">When using enums with associated values, it's often necessary to check for equality between two enum objects in some way. That can lead to boilerplate code like this:<br class="gmail_msg"></div><div class="gmail_msg" style="font-size:13px"><br class="gmail_msg"></div><div class="gmail_msg" style="font-size:13px">enum Option {</div><div class="gmail_msg" style="font-size:13px"> case foo(String)</div><div class="gmail_msg" style="font-size:13px"> case bar(Int)</div><div class="gmail_msg" style="font-size:13px"><span class="m_-8103148186215456657inbox-m_-1513968597867029764Apple-tab-span gmail_msg" style="white-space:pre-wrap"> </span>case zip</div><div class="gmail_msg" style="font-size:13px">}</div><div class="gmail_msg" style="font-size:13px"><br class="gmail_msg"></div><div class="gmail_msg" style="font-size:13px">func ==(lhs: Option, rhs: Option) -> Bool {</div><div class="gmail_msg" style="font-size:13px"> switch (lhs, rhs) {</div><div class="gmail_msg" style="font-size:13px"> case (.foo(let a), .foo(let b)) where a == b: return true</div><div class="gmail_msg" style="font-size:13px"> case (.bar(let a), .bar(let b)) where a == b: return true</div><div class="gmail_msg" style="font-size:13px"> case (.zip, .zip): return true</div><div class="gmail_msg" style="font-size:13px"> default: return false</div><div class="gmail_msg" style="font-size:13px"> }</div><div class="gmail_msg" style="font-size:13px">}</div><div class="gmail_msg" style="font-size:13px"><br class="gmail_msg"></div><div class="gmail_msg" style="font-size:13px">..which results in code duplication and opens the door to potential logic errors.</div><div class="gmail_msg" style="font-size:13px"><br class="gmail_msg"></div><div class="gmail_msg" style="font-size:13px">Instead, what if enums with associated values were automatically Equatable when all their associated values were Equatable? That would remove the need for such boilerplate code.</div><div class="gmail_msg" style="font-size:13px"><br class="gmail_msg"></div><div class="gmail_msg" style="font-size:13px">The Swift language guide states that custom classes and structs don't receive a default implementation of the == operator because the compiler can't guess what "equality" means for them. However, I think this could make sense for enums. An enum case, even with associated values, seems closer to a value itself than an object with logic and state.</div><div class="gmail_msg" style="font-size:13px"><br class="gmail_msg"></div><div class="gmail_msg" style="font-size:13px">I'd be interested to hear any thoughts on this. Would this be a beneficial addition?</div></div></div></blockquote><br class="gmail_msg"></div><div dir="auto" class="gmail_msg"><div class="gmail_msg">I think it makes more sense to come up with some syntax for reducing that kind of boilerplate code in general. In "pseudo-english", I'd write the == function as "if lhs and rhs are the same case && their associated values are the equal, return true, else return false".</div><div class="gmail_msg"><span style="background-color:rgba(255,255,255,0)" class="gmail_msg"><br class="gmail_msg"></span></div><div class="gmail_msg"><span style="background-color:rgba(255,255,255,0)" class="gmail_msg">What about doing something with the reflection system? Isn't that supposed to get overhauled for Swift 4? I'm not sure what the performance implications would be, though.</span></div><div class="gmail_msg"><span style="background-color:rgba(255,255,255,0)" class="gmail_msg"><br class="gmail_msg"></span></div><div class="gmail_msg"><span style="background-color:rgba(255,255,255,0)" class="gmail_msg">- Dave Sweeris </span></div></div>_______________________________________________<br class="gmail_msg">
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