indirect enum Foo { case Tail(int: Int, str: String) case Head(int: Int, str: String, foo: Foo) var int: Int { // switch書く } var str: String { // switch書く } var foo: Foo? { // switch書く } init(int: Int, str: String, foo: Foo?) { if let foo = foo { self = .Head(int: int, str: str, foo: foo) } else { self = .Tail(int: int, str: str) } } }