Sure, here's the start of the thread: 
https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151207/001856.html
 
<https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151207/001856.html>


> On Jan 3, 2016, at 9:10 PM, Matthew Johnson <[email protected]> wrote:
> 
> 
>> On Jan 3, 2016, at 9:08 PM, Drew Crawford <[email protected]> wrote:
>> 
>>> 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:
> 
> Can you point me to the source?  I would like more context around these 
> comments.
> 
>> 
>>> 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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