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

Kelvin Ma kelvin13ma at gmail.com
Mon Nov 20 19:48:45 CST 2017

the end goal here is to use tuples as a compatible currency type, to that
end it makes sense for these three protocols to be handled as “compiler
magic” and to disallow users from manually defining tuple conformances
themselves. i’m not a fan of compiler magic, but Equatable, Hashable, and
Comparable are special because they’re the basis for a lot of standard
library functionality so i think the benefits of making this a special
supported case outweigh the additional language opacity.

On Mon, Nov 20, 2017 at 8:42 PM, Chris Lattner <clattner at nondot.org> wrote:

> 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”?
> -Chris
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