@swift-5.1.5
struct StaticMember<Base> { init(_ base: Base) {} } protocol ColorStyle { typealias Member = StaticMember<Self> } protocol FontStyle { typealias Member = StaticMember<Self> } struct RedStyle : ColorStyle {} struct BlueStyle : ColorStyle {} struct RedFontStyle : FontStyle {} extension StaticMember where Base : ColorStyle { static var red: RedStyle.Member { print(self) return .init(.init()) } } extension StaticMember where Base : FontStyle { static var red: RedFontStyle.Member { print(self) return .init(.init()) } } protocol View {} extension View { func colorStyle<S : ColorStyle>(_ style: S.Member) {} func fontStyle<S: FontStyle>(_ style: S.Member) {} func anyStyle<S>(_ style: StaticMember<S>) {} } struct MyView : View {} MyView().colorStyle(.red) MyView().fontStyle(.red) MyView().anyStyle(.red)
