protocol P0 { } struct Type: P0 { } extension Array where Element: P0 { func test() { print("P0") } } extension Array where Element == Type { func test() { print("Type") } } let type = Array<Type>() type.test() // Type let p0 = Array<P0>() p0.test() /* iOSPlayground.playground:9:7: note: found this candidate func test() { ^ iOSPlayground.playground:15:7: note: found this candidate func test() { ^ */