Unless you need to abstract what the Factory class does, I would eliminate
AProto.
class Factory {
func constructInstance(_ t: T.Type) -> T
{
return t.init()
}
}
If you truly want to genericize Factory, you can do the following:
class Factory: AProto {
typealias ElementType = T
func constructInstance(_ t: T.Type) -> T {
return t.init()
}
}
However, ElementType can be inferred, so you can zap it, and then you get
this:
class Factory: AProto {
func constructInstance(_ t: T.Type) -> T {
return t.init()
}
}
…which compiles and I think does what you want it to. :)
Dan
On Wed, Jul 13, 2016 at 8:58 PM, Karl via swift-users wrote:
> So I’m trying to work generically to construct things based on their
> conformance to a protocol with an initialiser. I’m sure this worked before;
> I’ve done it before. Maybe there have been some changes in the language or
> something, because I’ve tried everywhich-way and this just isn’t flying:
>
> ==
> protocol AProto {
>
> associatedtype ElementType
> func constructInstance(_: ElementType.Type) -> ElementType
> }
>
> protocol SimpleConstructableElement {
> init()
> }
>
> extension Int : SimpleConstructableElement {}
>
> class Factory : AProto {
>
> typealias ElementType = SimpleConstructableElement
>
> func constructInstance(_ t: SimpleConstructableElement.Type) ->
> SimpleConstructableElement {
> return t.init()
> }
> }
>
> Factory().constructInstance(Int.self)
> =
>
> /tmp/MyPlayground.playground:15:7: Type 'Factory' does not conform to
> protocol 'AProto'
> /tmp/MyPlayground.playground:6:7: Protocol requires function
> 'constructInstance' with type '(ElementType.Protocol) -> ElementType'
> /tmp/MyPlayground.playground:19:7: Candidate has non-matching type
> '(SimpleConstructableElement.Type) -> SimpleConstructableElement’
>
> =
>
>
> The thing that gets me about this is that Xcode’s code-completion tells me
> that SimpleConstructableElement.Type is of type
> SimpleConstructableElement.Protocol, so it should be the same as
> ElementType.Protocol and should be accepted, right?
>
> Karl
> ___
> swift-users mailing list
> swift-users@swift.org
> https://lists.swift.org/mailman/listinfo/swift-users
>
___
swift-users mailing list
swift-users@swift.org
https://lists.swift.org/mailman/listinfo/swift-users
