It's pretty bizarre that conforming to `protocol P: Q {}` requires an explicit
conformance to Q when Q is a class but not when Q is a protocol. It's the same
syntax, but conformance is only "inherited" for protocols.
> On Feb 1, 2017, at 3:47 PM, Matthew Johnson via swift-evolution
> <[email protected]> wrote:
>
>
>
> Sent from my iPad
>
>> On Feb 1, 2017, at 5:11 PM, David Sweeris via swift-evolution
>> <[email protected]> wrote:
>>
>>
>>> On Feb 1, 2017, at 3:01 PM, David Hart via swift-evolution
>>> <[email protected]> wrote:
>>>
>>>
>>> On 1 Feb 2017, at 22:54, Douglas Gregor <[email protected]> wrote:
>>>
>>>>
>>>>> On Jan 29, 2017, at 8:44 PM, Slava Pestov via swift-evolution
>>>>> <[email protected]> wrote:
>>>>>
>>>>> This is a nice generalization of the existing protocol composition
>>>>> syntax. Implementation might get a little tricky — this touches a lot of
>>>>> things, such as inheritance clauses, constraints in generic signatures,
>>>>> and casts. It would require thorough testing.
>>>>>
>>>>> There are also a few odd corner cases to sort out:
>>>>>
>>>>> typealias T = SomeClass & SomeProtocol
>>>>>
>>>>> class C : T { // should we allow this? probably yes
>>>>> }
>>>>>
>>>>> protocol P : T { // should we allow this? probably no
>>>>> }
>>>>
>>>> IIRC, we already allow the latter where T is a typealias for SomeProtocol1
>>>> & SomeProtocol2. Why not allow it generally?
>>>
>>> Well what would it mean? A protocol can't inherit or conform to a class.
>>
>> That anything which conforms to that protocol must subclass SomeClass?
>
> Yes, this is exactly what I would expect. I was calling it a supertype
> requirement earlier in the thread.
>
>>
>> - Dave Sweeris
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