[swift-evolution] [Discussion] Generic protocols

[Anders Ha]

This is called generalized existentials. It is included in the Generic Manifesto, has been discussed quite a few times with long email chains before, and spawned the change to the `protocol<>` syntax as kinda a precursor. It would be surprised if Swift 4 Phase 2 doesn't have it given its popularity.

Regards
Anders

> On 2 Dec 2016, at 20:13, Charles Srstka via swift-evolution <swift-evolution at swift.org> wrote:
> 
>> On Dec 2, 2016, at 12:34 PM, Adrian Zubarev via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> I just overlooked that the subsection about generic protocols was inside the Unlikely section.
>> 
>> The problem is that I need a way to refer to a function with a specific name. Plus the connection type has to have a specific API, like having a DispatchQueue and know the router object if there is any (sounds like a protocol right?!). The function reference should also keep the connection object alive with a strong reference. 
>> 
>> associatedtype does not solve that problem for me.
>> 
>> I clearly see that generic protocols overlap with associatedtype but couldn’t we find a compromise here? For instance like Chris Lattner introduced generic type aliases without the ability of constants.
>> 
> 
> Why don’t we just use angle brackets to specify associated types? Protocols aren’t using them for anything anyway. Then you could:
> 
> if let someSequence as? Sequence<Iterator.Element == Int> { // do something }
> 
> which would form a nice parallel to the syntax for casting things to generic types.
> 
> Charles
> 
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