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

[Mike Kluev]

On 25 November 2017 at 23:07, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:

> Not sure what you’re asking. Equatable is a protocol.
>

that's the point. i mean, if user writes this:

extension (Equatable, Equatable) : Equatable

what *else* could he mean other than this:

extension <T: Equatable, R: Equatable> (T, R) : Equatable

and if it is indeed the only reasonable meaning we can think of - i'd say
the first notation is nicer.


> For a protocol P, (P, P) is a concrete type with two elements each of
> existential type P.
>

this part i do not understand. protocol is not an existential type. or is
it?


> For a type T : P, a tuple of type (T, T) is not a tuple of type (P, P). If
> we can extend tuples, you can write a generic algorithm that works with any
> type (T, T) where T : P, and/or you can write an algorithm that works with
> concrete type (P, P). Note that there is no overlap between these two
> because existential type P does not conform to protocol P.
>
>
Mike
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