> Existentials for protocols with Self and / or associated type requirements 
> would require bindings for Self and / or the associated type(s).  At least 
> when you use a member that contains Self and / or an associated type in its 
> signature.  So the previous example will always fail to compile. 

Not true.  Joe Groff:

> This seems like it would be addressed just by allowing Factory to be used as 
> a dynamic type, with its Product type generalized to Any. We'll be set up to 
> support that with some runtime work to store associated types in protocol 
> witness tables (which is also necessary to fix cyclic conformances, one of 
> our Swift 3 goals).


> Yeah, when generalizing a protocol type, we ought to be able to either 
> generalize the associated types to their upper bounds, for use cases like 
> yours, or constrain them to specific types, for the AnyGenerator<T> kind of 
> case.




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