[swift-evolution] [Proposal] Tuple Extensions

[Joe Groff]

> On May 3, 2016, at 10:06 PM, Robert Widmann <devteam.codafi at gmail.com> wrote:
> 
> Once-and-for-all implementations come in many flavors.  For now, we have clear interest in making a limited subset of possible tuples properly Comparable.  This will also make it easier to implement extensions to specific arities now and serve as a base for variadic generics if that is the path we take.  I could certainly see Future Swift™ allowing this to sit side-by-side with the finite version in this proposal, couldn't you?
> 
> extension (T...) : Equatable where T.Element : Equatable { }
> 
> func == <T : Equatable>(l : (T...), r : (T...)) -> Bool { /* .. */ }

One problem with introducing variadics later would be that, if we ship the specific-arity conformances in an ABI-stable standard library, we're stuck carrying those extensions around forever for backward compatibility.

-Joe

> ~Robert Widmann
> 
> 2016/05/04 0:54、Joe Groff <jgroff at apple.com> のメッセージ:
> 
>> 
>>> On May 3, 2016, at 9:52 PM, Robert Widmann <devteam.codafi at gmail.com> wrote:
>>> 
>>> Trouble is that I don't want variadic generics without corresponding support from the type system which is untenable without HKTs (see last paragraph of proposal).  C++'s variadic implementation of std::tuple is not elegant to my mind, and would have no place in a library I could think of writing.
>> 
>> I think we'd keep tuples as a builtin type. Variadics would just let you implement Equatable/Hashable/etc. once for all tuple arities. I don't see why we'd need HKTs for that.
>> 
>> -Joe