> On 24 Jan 2017, at 01:13, Jonathan Hull via swift-evolution
> <swift-evolution@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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IMO, the way to do this is by nesting the struct inside the protocol (not
possible yet). For example, the standard library contains EmptyCollection and
CollectionOfOne. I think the way to express such things would be as:
Collection.Empty<T> and Collection.One<T>.
Not promising anything about the stdlib interface itself, but in general I
think these kind of canned conformances are ideal candidates for nesting. So in
your case you might have X.Default (or something more meaningful).
- Karl
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