exampleを引用
protocol P { } extension Int: P { } // Fully supported: Set unconditionally conforms to P extension Set: P { } // Not supported in dynamic casts: Array conforms to P // only when its element conforms to P extension Array: P where Element: P { } func castToP(_ value: Any) { if value is P { print("\(type(of: value)) conforms to P"); } else { print("\(type(of: value)) does not conform to P") } } castToP(Set([1, 2, 3])) // unconditional conformances // are supported: // prints "Set<Int> conforms to P castToP([1, 2, 3]) // unsupported conditional conformance: // incorrectly prints "Array<Int> does not // conform to P" castToP([3.141593, 2.71828]) // unsupported conditional conformance: // correctly prints "Array<Double> does not // conform to P"
(edited)