protocol Costume { func withBells() -> Self func hasSameAdornments(as other: Self) -> Bool } func hasBells<C: Costume>(_ costume: Costume) -> Bool { return costume.hasSameAdornments(as: costume.withBells()) }protocol Costume { func withBells() -> Self func hasSameAdornments(as other: Self) -> Bool } func hasBells<C: Costume>(_ costume: Costume) -> Bool { return costume.hasSameAdornments(as: costume.withBells()) }func checkFinaleReadiness(costumes: [any Costume]) -> Bool { for costume in costumes { if !hasBells(costume) { // okay with this proposal: C is bound to the type stored inside the 'any' box, known only at runtime return false } } return true } ↑これができるようになるfunc checkFinaleReadinessOpenCoded(costumes: [any Costume]) -> Bool { for costume: some Costume in costumes { // implicit generic parameter binds to underlying type of each costume let costumeWithBells = costume.withBells() // returned type is the same 'some Costume' as 'costume' if !costume.hasSameAdornments(costumeWithBells) { // okay, 'costume' and 'costumeWithBells' have the same type return false } } return true } ↑これもできるようにするって書いてあるのかな・・・？any P に対して Self を返すメソッドを呼び出すと、 some P として返ってくるfunc cannotOpen1<T: P>(_ array: [T]) { .. } func cannotOpen2<T: P>(_ a: T, _ b: T) { ... } func cannotOpen3<T: P>(_ values: T...) { ... } struct X<T> { } func cannotOpen4<T: P>(_ x: X<T>) { } func cannotOpen5<T: P>(_ x: T, _ a: T.A) { } func cannotOpen6<T: P>(_ x: T?) { } func testCannotOpenMultiple(array: [any P], p1: any P, p2: any P, xp: X<any P>, pOpt: (any P)?) { cannotOpen1(array) // each element in the array can have a different underlying type, so we cannot open cannotOpen2(p1, p2) // p1 and p2 can have different underlying types, so there is no consistent binding for 'T' cannotOpen3(p1, p2) // similar to the case above, p1 and p2 have different types, so we cannot open them cannotOpen4(xp) // cannot open the existential in 'X<any P>' there isn't a specific value there. cannotOpen5(p1, p2.getA()) // cannot open either argument because 'T' is used in both parameters cannotOpen6(pOpt) // cannot open the existential in '(any P)?' because it might be nil, so there would not be an underlying type } ↑ structural position だと P のオブジェクトの数が動的になるから open できない