Guard

Guard.swift

protocol Guard {}
class Adam: Guard {}
class Alfred: Adam {}

func conforms1<T>(x: Any.Type, y: T.Type) -> Bool {
    return x is T.Type
}

// This also should be true but for some reason type is Guard.Protocol instead of Guard.Type.
print(conforms1(Adam.self, y: Guard.self))
print(conforms1(Adam.self, y: Adam.self))
print(conforms1(Alfred.self, y: Adam.self))

print("---")

func conforms2<T>(x: Any.Type, y: T.Type) -> Bool {
    return x is T
}

print(conforms2(Adam.self, y: Guard.Type.self))
print(conforms2(Adam.self, y: Adam.Type.self))
print(conforms2(Alfred.self, y: Adam.Type.self))

// Assume this is expensive operation and I want to call only once I know it has a type I want.
let obj: () -> Any = { Alfred() }

func conforms1<T>(x: Any.Type, y: T.Type, obj: () -> Any) -> T? {
    if x.dynamicType is T.Type.Type {
        return obj() as? T
    } else {
        return nil
    }
}

print(conforms1(Adam.self, y: Guard.self, obj: obj))
print(conforms1(Adam.self, y: Adam.self, obj: obj))
print(conforms1(Alfred.self, y: Adam.self, obj: obj))

print("---")

func conforms2<T>(x: Any.Type, y: T.Type.Type, obj: () -> Any) -> T? {
    if x is T.Type {
        return obj() as? T
    } else {
        return nil
    }
}

// print(conforms2(Adam.self, y: Guard.Type.self, obj: obj)) // Everything is good, except for the compiling error of Protocol & Type mismatch here.
print(conforms2(Adam.self, y: Adam.Type.self, obj: obj))
print(conforms2(Alfred.self, y: Adam.Type.self, obj: obj))