[swift-evolution] [swift-evolution-announce] [Review] SE-0089: Replace protocol<P1, P2> syntax with Any<P1, P2>

[Dave Abrahams]

on Wed Jun 08 2016, Jordan Rose <swift-evolution at swift.org> wrote:

>> On Jun 8, 2016, at 13:16, Dave Abrahams via swift-evolution
>> <swift-evolution at swift.org> wrote:
>> 
>> 
>> on Wed Jun 08 2016, Thorsten Seitz
>
>> <swift-evolution at swift.org
>> <mailto:swift-evolution at swift.org>>
>> wrote:
>> 
>>> Ah, thanks, I forgot!  I still consider this a bug, though (will have
>>> to read up again what the reasons are for that behavior).
>> 
>> Yes, but in the case of the issue we're discussing, the choices are:
>> 
>> 1. Omit from the existential's API any protocol requirements that depend
>>   on Self or associated types, in which case it *can't* conform to
>>   itself because it doesn't fulfill the requirements.
>> 
>> 2. Erase type relationships and trap at runtime when they don't line up.
>> 
>> Matthew has been arguing against #2, but you can't “fix the bug” without
>> it.
>
> #1 has been my preference for a while as well, at least as a starting
> point. 

I should point out that with the resyntaxing of existentials to
Any<Protocols...>, the idea that Collection's existential doesn't
conform to Collection becomes far less absurd than it was, so maybe this
is not so bad.

-- 
Dave