Protocol func returning Self

Question

I have a protocol P that returns a copy of the object:

protocol P {
    func copy() -> Self
}

and a class C that implements P:

Answer 1

Actually, there is a trick that allows to easily return Self when required by a protocol (gist):

/// Cast the argument to the infered function return type.
func autocast(some: Any) -> T? {
    return some as? T
}

protocol Foo {
    static func foo() -> Self
}

class Vehicle: Foo {
    class func foo() -> Self {
        return autocast(Vehicle())!
    }
}

class Tractor: Vehicle {
    override class func foo() -> Self {
        return autocast(Tractor())!
    }
}

func typeName(some: Any) -> String {
    return (some is Any.Type) ? "\(some)" : "\(some.dynamicType)"
}

let vehicle = Vehicle.foo()
let tractor = Tractor.foo()

print(typeName(vehicle)) // Vehicle
print(typeName(tractor)) // Tractor