Forgive me if this has already come up, but since we’re talking about fixing generics, I wonder if there is any solution in the pipeline for this problem:
-- protocol P { func foo() } struct S: P { func foo() { print("foo") } } func doSomething<C: CollectionType where C.Generator.Element: P>(c: C) { for each in c { each.foo() } } let arr: [P] = [S()] doSomething(arr) // error: cannot invoke 'doSomething' with an argument list of type '([P])’ -- Why is this an error? The whole definition of [P] is basically an array of things that conform to P. Isn’t that exactly what “where Element: P” is asking for? Changing Element: P to Element == P solves this particular issue, of course, but then passing something like [S] to the array will fail. The result is that you need to write two functions, and either have one eat the performance cost of constructing a new array that has the correct static type to pass to the other (since, unlike arrays, I can’t figure out a way to convert “Collection where Element: P” into “Collection where Element == P” with a simple cast), or just fill it with the dreaded copy-paste code. Neither seems ideal. Charles _______________________________________________ swift-evolution mailing list swift-evolution@swift.org https://lists.swift.org/mailman/listinfo/swift-evolution