> On 7 Feb 2017, at 06:05, Slava Pestov <[email protected]> wrote:
>
>>
>> On Feb 6, 2017, at 9:00 PM, Karl Wagner via swift-evolution
>> <[email protected] <mailto:[email protected]>> wrote:
>> - Nested protocols in generic types are not parameterised by the parent's
>> generic parameters.
> So if I write GenericType<Int>.SomeProto and GenericType<String>.SomeProto,
> is it the same protocol? What about GenericType.SomeProto, is that allowed?
>
> Slava
GenericType.SomeProto (without parameters) is the only spelling that is
allowed. There is no GenericType<Int>.SomeProto.
That way we avoid every bound-generic type creating a new protocol.
I think it works really nicely when you consider what it would like like with
existential-based capturing. Notice that there is only one
‘MyCollectionView.Source’, and compatibility is determined based on existential
constraints.
- Karl
class MyCollectionView<MediaItem> : UICollectionView {
protocol Source {
// [implicit] associatedtype MediaItem
func item(at: Int) -> MediaItem
var numberOfItems: Int { get }
}
var source: Any<MyCollectionView.Source where .MediaItem == MediaItem> //
Not possible today.
}
class BookSource: MyCollectionView.Source {
typealias MediaItem = Book
func item(at: Int) -> Book { /* ... */ }
var numberOfItems: Int { /* ... */ }
}
class DummySource<MediaItem>: MyCollectionView.Source where MediaItem:
DummyConstructable {
// associatedtype 'MediaItem' bound to generic parameter.
func item(at: Int) -> MediaItem { /* ... */ }
var numberOfItems: Int { /* ... */ }
}
MyCollectionView<Book>().source = BookSource()
MyCollectionView<Book>().source = DummySource<Book>()
MyCollectionView<Song>().source = DummySource() // type is: DummySource<Song>
MyCollectionView<Movie>().source = DummySource() // type is: DummySource<Movie>
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