[swift-evolution] two protocols with the same method name

[品雪]

Good point.

Protocol is a contract, it is natural to allow same item in multiple
protocol and eventually pointing to one single implementation.

By giving warning simply for same name, it will be quite annoying when the
project run into this situation without any wrong. For example:


protocol ForwardIndexType : _Incrementable {

    @warn_unused_result

    public func advancedBy(n: Self.Distance) -> Self

}


extension ForwardIndexType {

    @warn_unused_result

    public func advancedBy(n: Self.Distance) -> Self

    @warn_unused_result

    public func advancedBy(n: Self.Distance, limit: Self) -> Self

    @warn_unused_result

    public func distanceTo(end: Self) -> Self.Distance

}


protocol BidirectionalIndexType : ForwardIndexType

extension BidirectionalIndexType {

    @warn_unused_result

    public func advancedBy(n: Self.Distance) -> Self

    @warn_unused_result

    public func advancedBy(n: Self.Distance, limit: Self) -> Self

}


If a type conforms BidirectionalIndexType, it gets all these advancedBy().
OK, for this specific case we may workaround by assuming safe for those
inherited. Which means we only warn for same name item from protocols in
different protocol hierarchy without common root.


It is still doubtful even for this filtered case, because compiler cannot
tell it appears by intention or by mistake. We have to suppress it for
acceptable cases, that's annoying as protocol should allow it naturally.


There is a case good for throwing error: receiving item with same name but
different type from two protocols, but it is already an error now.



On Sat, Jan 9, 2016 at 11:47 AM, Wallacy via swift-evolution <
swift-evolution at swift.org> wrote:

> Storage properties on protocol or in extension plus something when call
> maybe a solution:
>
>        protocol Marriageable {
>                var foo:Int = 0; // actual a var.
>                 var ring: String? // actual a var.
>         }
>         protocol CallReceivable {
>                 var ring: String? // actual a var.
>         }
>
>         struct Person: Marriageable, CallReceivable { }
>
> OR
>         protocol Marriageable {
>                 var ring: String? { get set }
>         }
>         protocol CallReceivable {
>                 var ring: String? { get set }
>         }
>
>         struct Person { }
>
>        extension Person: Marriageable{
>          var ring: String?
>        }
>
>      extension Person: CallReceivable{
>          var ring: String?
>        }
>
> So:
>
> var person = Person()
> person.foo = 1 // ok
>
> person.ring = getRingtone() // error, ring is ambiguous
> (person as CallReceivable).ring = getRingtone()  // ok
> OR
> person.CallReceivable.ring = getRingtone()  // ok | CallReceivable is a
> know person protocol, so can get a implicity dot notation,
> like .dynamicType.staticMethod();
>
> Anyway, it's not an easy problem to solve.
>
> Em sáb, 9 de jan de 2016 às 01:09, Brent Royal-Gordon via swift-evolution <
> swift-evolution at swift.org> escreveu:
>
>> > I don’t really get what you are driving at.
>>
>> The point is that, although `A` and `B` both require properties with the
>> same name, they expect different semantics from that property. Let's maybe
>> give these more concrete names so you can understand the idea:
>>
>>         protocol Marriageable {
>>                 var ring: String? { get set }   // File name of image of
>> this person's wedding ring.
>>         }
>>         protocol CallReceivable {
>>                 var ring: String? { get set }   // File name of ringtone
>> to be used for this person.
>>         }
>>
>>         struct Person: Marriageable, CallReceivable {
>>                 var ring: String?
>>         }
>>
>> Of course a person is marriageable and can this have "a ring", and of
>> course you can also receive a call from them and they can thus have "a
>> ring". But in reality, the "ring" that satisfies one of these things will
>> not work for the other. If your best friend gets married and you add an
>> image of the ring, then the next time your friend calls you, the phone
>> ringing screen will try to play a JPEG as an MP3.
>>
>> The "ring" example is, of course, slightly contrived, but I'm sure you
>> can imagine a similar problem with real names, where you end up using the
>> same term for two different and incompatible things.
>>
>> What the OP is basically asking is, when Swift sees the same type
>> conforming to Marriageable and CallReceivable, should it optimistically
>> assume that the `ring` properties they both require are compatible and
>> allow the code to pass through without comment? Or should it
>> pessimistically assume that the `ring` properties are incompatible and emit
>> a warning or error about them?
>>
>> --
>> Brent Royal-Gordon
>> Architechies
>>
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>
>
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>
>


-- 
Best Regards!

Yang Wu
--------------------------------------------------------
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