[swift-evolution] Enhanced existential types proposal discussion

[Austin Zheng]

I agree; the difference between protocols with and without associated types has been an endless source of confusion for a lot of people.

Speaking of which, for those who care I rewrote the draft proposal to attempt a much more rigorous treatment of the semantics of the generalized existential, including a discussion about existential type equivalence and subtyping. It would be nice to see people poke holes in my logic so I can patch them up. https://github.com/austinzheng/swift-evolution/blob/az-existentials/proposals/XXXX-enhanced-existentials.md <https://github.com/austinzheng/swift-evolution/blob/az-existentials/proposals/XXXX-enhanced-existentials.md>

Austin

> On May 22, 2016, at 3:05 PM, Russ Bishop via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 
>> On May 17, 2016, at 1:55 PM, Joe Groff via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> I agree with this. If we're certain we should reskin protocol<> as Any<>, we should frontload that change—in addition to affecting source code, it'd also influence the runtime behavior of type printing/parsing, which can't be statically migrated in the future. I think any discussion of extending existentials has to be considered out of scope for Swift 3, though, so the Any rename deserves its own proposal.
>> 
>> -Joe
> 
> 
> Its really unfortunate that the generics work is probably going to be deferred. When you really dive in to protocol-oriented programming and designing frameworks to be native Swift (taking advantage of Swift features) the existential problem comes up a lot and leads to sub-optimal designs, abandonment of type safety, or gobs of boilerplate.  
> 
> 
> Russ
> 
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