swift-bug.swift

protocol A {
    func foo() -> Int
}

extension A {
    func foo() -> Int {
        return 10
    }
}

class BaseOne: A {
    func foo() -> Int {
        return 20
    }
}

class ChildOne: A {
    func foo() -> Int {
        return 200
    }
}

class BaseTwo: A {
    
}

class ChildTwo: BaseTwo {
    func foo() -> Int {
        return 30
    }
}

BaseOne().foo()          // Print 20
(BaseOne() as A).foo()   // Print 20
ChildOne().foo()         // Print 200
(ChildOne() as A).foo()  // Print 200
ChildTwo().foo()         // Print 30
(ChildTwo() as A).foo()  // Print 10 !!!! (Must be 30)