@swift-5.3.3
struct MySet<Element: Hashable> { private var _set: Set<Element> } extension MySet: Collection { subscript(idx: Set<Element>.Index) -> Element { _set[idx] } var startIndex: Set<Element>.Index { _set.startIndex } var endIndex: Set<Element>.Index { _set.endIndex } func index(after i: Set<Element>.Index) -> Set<Element>.Index { _set.index(after: i) } }