[swift-evolution] Default implementation of protocols

[Jonathan Hull]

I agree with your point on classes, so maybe just value types would be allowed to do it (I have only wanted it for structs myself).  I think I answered your comment about distinguishing between existential and struct X if you re-read my original message.

Thanks,
Jon

> On Jan 23, 2017, at 5:10 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
> 
> This would get very confusing, as it would be impossible for a class to distinguish conforming to protocol X vs. inheriting from base class X, or else we would have to change the spelling for that as well. Moreover, you would have no way of distinguishing the existential X from the struct X. I see nothing wrong with the clarity afforded by naming the distinct things `FooProtocol` and `Foo`, and I disagree that there's anything "simplifying" about naming two different things with one name.
> 
> 
> On Mon, Jan 23, 2017 at 6:13 PM, Jonathan Hull via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> Have we considered allowing a struct/class/enum to have the same name as a protocol as long as it conforms to the protocol?  Type declarations would have to always mean the protocol (which includes the concrete type as well).  Static functions would always apply to the concrete type.
> 
> Seems like a good way to support having a default implementation of a protocol.  I am always running into the awkward naming issues around this...
> 
>         protocol X {
>                 //yada yada
>         }
> 
>         struct X { //Implicitly adheres to protocol X (because it must)
>                 init(){…}
>         }
> 
>         let myVar:X //This refers to the protocol
>         let otherVar = X() //This makes the struct
> 
> If we do need to be able to spell the concrete type for other uses, we could probably do something like: ‘concrete(X)’ which isn’t pretty, but is there for the rare times it is needed for utility.  I can’t think of any reason except making an array of the concrete type.
> 
> I am guessing there is a subtle technical reason this won’t work, but I wanted to mention it now just in case it is possible.  Seems like it could have a large (simplifying) effect on the namespace of the standard library.
> 
> Thanks,
> Jon
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