[swift-evolution] [Draft] Allow multiple conformances to the same protocol

[Антон Жилин]

Right. If associated type has the same value for both conformances, then
everything should be fine. Fixed that example.

- Anton

2016-06-13 0:15 GMT+03:00 Dan Appel <dan.appel00 at gmail.com>:

> >if our protocol conforms to a protocol with associated type requirements,
> then we still can't conform to our protocol multiple times.
>
> I don't think so:
>
> protocol A {
>
>     associatedtype TypeA
>
> }
>
>
> protocol B<TypeB>: A {
>
>     func convert(from: TypeB) -> TypeA
>
> }
>
>
> struct C: A {
>
>     typealias TypeA = String
>
> }
>
> extension C: B<Int> {
>
>     func convert(from int: Int) -> String {
>
>         return String(int)
>
>     }
>
> }
>
> extension C: B<Double> {
>
>     func convert(from double: Double) -> String {
>
>         return String(double)
>
>     }
>
> }
>
> Seems to me like the above should work fine: the associated type is
> declared once, but the generic protocol is conformed to multiple times.
>
> On Sun, Jun 12, 2016 at 1:22 PM Антон Жилин <antonyzhilin at gmail.com>
> wrote:
>
>> Copy of link to the proposal:
>>
>> https://github.com/Anton3/swift-evolution/blob/generic-protocols/proposals/NNNN-generic-protocols.md
>>
>> Inline:
>>
>> 2016-06-12 21:51 GMT+03:00 Dan Appel <dan.appel00 at gmail.com>:
>>
>>> Awesome that you guys started this! I've been meaning to pitch it for a
>>> while. Couple notes:
>>>
>>> - in the motivation, you're conforming to SequenceType while defining a
>>> From protocol (just a typo I think)
>>>
>>
>> Fixed
>>
>>
>>> - the proposal should mention Brent's comments since it doesn't have a
>>> rebuttal to the "unlikely" status generic protocols were given in the
>>> generic manifesto. Brent does a great job of doing that
>>>
>>
>> Added a bold link
>>
>>
>>> - is there a way for generic protocols to still have associated types? I
>>> think that could have some interesting use cases.
>>>
>>
>> Generic protocols can contain associated types, but no type can conform
>> to multiple instances of such protocols.
>>
>> Actually, this limitation is more restricting than it seems, because if
>> our protocol conforms to a protocol with associated type requirements, then
>> we still can't conform to our protocol multiple times.
>>
>>
>>> Dan Appel
>>>
>>> On Sun, Jun 12, 2016 at 11:28 AM Антон Жилин <swift-evolution at swift.org>
>>> wrote:
>>>
>> Yes, everything that works on generic types should work for generic
>>>> protocols. I'll add that.
>>>>
>>>> What won't work is declaring that  MyComparable : Comparable  iff  T ==
>>>> Self. The same won't work for current non-generic protocols as well.
>>>> Although that feature is highly requested, it is discussed in a
>>>> separate proposal.
>>>>
>>>> - Anton
>>>>
>>>> 2016-06-12 21:16 GMT+03:00 Xiaodi Wu <xiaodi.wu at gmail.com>:
>>>>
>>>>>
>>>>>
>>>>> On Sun, Jun 12, 2016 at 8:01 AM, Антон Жилин <
>>>>> swift-evolution at swift.org> wrote:
>>>>>
>>>>>> I've prepared a proper draft:
>>>>>>
>>>>>>
>>>>>> https://github.com/Anton3/swift-evolution/blob/generic-protocols/proposals/NNNN-generic-protocols.md
>>>>>>
>>>>>>
>>>>> When you propose this:
>>>>> Syntax in protocol extensions
>>>>>
>>>>> protocol MyComparable<T> {
>>>>>   func < (left: Self, right: T)
>>>>> }extension MyComparable {
>>>>>   func > (left: T, right: Self) {
>>>>>     return right < left
>>>>>   }
>>>>> }
>>>>>
>>>>>
>>>>> Would it be possible for me to write something like:
>>>>>
>>>>> ```
>>>>> extension MyComparable<T : SignedNumber> { ... }
>>>>> ```
>>>>>
>>>>
>>>> _______________________________________________
>>>> swift-evolution mailing list
>>>> swift-evolution at swift.org
>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>
>>> --
>>> Dan Appel
>>>
>> --
> Dan Appel
>
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