> On Dec 5, 2016, at 11:39 AM, Joe Groff <jgr...@apple.com> wrote:
>
>> On Dec 4, 2016, at 6:46 PM, Charles Srstka via swift-evolution
>> <swift-evolution@swift.org> wrote:
>>
>> The following currently does not work:
>>
>> protocol P: class {}
>> class C: P {}
>>
>> func foo<T>(t: T) where T: AnyObject {
>> print("foo")
>> }
>>
>> let p: P = C()
>>
>> foo(t: p) // error: cannot invoke 'foo' with an argument list of type '(t:
>> P)'
>>
>> It seems to me that this ought to have been allowed, since P is declared as
>> being a reference type and thus should have been able to satisfy the
>> function’s requirements.
>>
>> Is this worthy of writing a language proposal, or would this be considered a
>> bug that should be sent through the radar system instead?
>
> It's a limitation of the current implementation. `AnyObject` is taken as
> meaning that a conforming type has a representation that consists of a single
> refcounted pointer. Protocol existentials do not have a single-refcounted
> representation since the witness table for the conformances must also be
> carried around, therefore the protocol type does not conform to AnyObject's
> representation requirement.
Is there any way to just say “This function takes any reference type” that will
work?
Charles
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