<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Nov 28, 2017 at 12:59 PM, Joe Groff via swift-evolution <span dir="ltr"><<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span class=""><br>
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> On Nov 28, 2017, at 10:52 AM, Vladimir.S <<a href="mailto:svabox@gmail.com">svabox@gmail.com</a>> wrote:<br>
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> On 27.11.2017 20:28, Joe Groff via swift-evolution wrote:<br>
>>> On Nov 20, 2017, at 5:43 PM, Chris Lattner via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.<wbr>org</a>>> wrote:<br>
>>><br>
>>><br>
>>>> On Nov 20, 2017, at 5:39 PM, Kelvin Ma via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.<wbr>org</a>>> wrote:<br>
>>>><br>
>>>> when SE-185 <<a href="https://github.com/apple/swift-evolution/blob/master/proposals/0185-synthesize-equatable-hashable.md" rel="noreferrer" target="_blank">https://github.com/apple/<wbr>swift-evolution/blob/master/<wbr>proposals/0185-synthesize-<wbr>equatable-hashable.md</a>> went through swift evolution, it was agreed that the next logical step <<a href="https://www.mail-archive.com/swift-evolution@swift.org/msg26162.html" rel="noreferrer" target="_blank">https://www.mail-archive.com/<wbr>swift-evolution@swift.org/<wbr>msg26162.html</a>> is synthesizing these conformances for tuple types, though it was left out of the original proposal to avoid mission creep. I think now is the time to start thinking about this. i’m also tacking on Comparable to the other two protocols because there is precedent in the language from SE-15 <<a href="https://github.com/apple/swift-evolution/blob/master/proposals/0015-tuple-comparison-operators.md" rel="noreferrer" target="_blank">https://github.com/apple/<wbr>swift-evolution/blob/master/<wbr>proposals/0015-tuple-<wbr>comparison-operators.md</a>> that tuple comparison is something that makes sense to write.<br>
>>>><br>
>>>> EHC conformance is even more important for tuples than it is for structs because tuples effectively have no workaround whereas in structs, you could just manually implement the conformance.<br>
>>><br>
>>> In my opinion, you’re approaching this from the wrong direction. The fundamental problem here is that tuples can’t conform to a protocol. If they could, synthesizing these conformances would be straight-forward.<br>
>> It would be a tractable intermediate problem to introduce built-in conformances for tuples (and perhaps metatypes) to Equatable/Hashable/Comparable without breaching the more general topic of allowing these types to have general protocol conformances. I think that would cover the highest-value use cases.<br>
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> So, shouldn't we do this first step ASAP and then design a good common solution to allow tuples/metatypes/funcs to confirm to custom protocols in some next version of Swift?<br>
> I really believe this is the good practical decision and will be supported by community if such proposal will be on the table.<br>
> Is there any drawback in such step?<br>
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</span>The expected behavior of tuple Equatable/Hashable/Comparable seems obvious to me (though I could well be missing something), and any behavior we hardcode should be naturally replaceable by a generalized conformance mechanism, so it's primarily a "small matter of implementation". There would be some implementation cost to managing the special case in the compiler and runtime; the tradeoff seems worth it to me in this case, but others might reasonably disagree. Not speaking for the entire core team, I would personally support considering a proposal and implementation for builtin tuple Equatable/Hashable/Comparable conformance.<br>
<div class="HOEnZb"><div class="h5"><br>
-Joe<br>
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