[swift-evolution] Synthesizing Equatable, Hashable, and Comparable for tuple types

Chris Lattner clattner at nondot.org
Mon Nov 20 19:42:53 CST 2017

> On Nov 20, 2017, at 5:39 PM, Kelvin Ma via swift-evolution <swift-evolution at swift.org> wrote:
> when SE-185 <https://github.com/apple/swift-evolution/blob/master/proposals/0185-synthesize-equatable-hashable.md> went through swift evolution, it was agreed that the next logical step <https://www.mail-archive.com/swift-evolution@swift.org/msg26162.html> 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 <https://github.com/apple/swift-evolution/blob/master/proposals/0015-tuple-comparison-operators.md> that tuple comparison is something that makes sense to write.
> 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. 

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.

If you’re interested in pushing this forward, the discussion is “how do non-nominal types like tuples and functions conform to protocols”?


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