Extension doesn't go in derived class in swift

Question

I am implementing a protocol and providing some optional methods in swift but then I am implement these optional methods in derived class. When I call a protocol method it is calling extension method not the derived class method.

protocol ProtocolA {
    func method1()
    // Optional
    func method2()
}
extension ProtocolA {
    func method2(){
        // It comes here, instead of class B method2.
        print("In method 2 - Protocol A")
    }
}

class A : ProtocolA {
    func method1() {
        print("In method 1 - class A")
    }
}

class B : A {
    func method2() {
        print("In method 2 - Class B")
    }
}

var a : A = B()
// It should call - In method 2 - Class B but the output is "In method 2 - Protocol A"
a.method2()

Possible answer: http://stackoverflow.com/questions/31795158/swift-2-protocol-extension-not-calling-overriden-method-correctly — Ozgur Vatansever, Jan 01 '16 at 05:01
So do you need an answer then? The solution I showed is far from perfect but in your case another one could fit better. — Qbyte, Jan 01 '16 at 11:05

score 0 · Answer 1 · answered Feb 17 '16 at 20:41

First you should implement the method on Class A for on class B you can override the method for example:

protocol ProtocolA {
    func method1()
    // Optional
    func method2()
}
extension ProtocolA {
    func method2(){
        // It comes here, instead of class B method2.
        print("In method 2 - Protocol A")
    }
}

class A : ProtocolA {
    func method1() {
        print("In method 1 - Class A")
    }

    func method2(){
        // It comes here, instead of class B method2.
        print("In method 2 - Class A")
    }
}

class B : A {
    override func method2() {
        print("In method 2 - Class B")
    }
}

var a : A = B()
a.method2()

or use the class B as a Type directly:

protocol ProtocolA {
    func method1()
    // Optional
    func method2()
}
extension ProtocolA {
    func method2(){
        // It comes here, instead of class B method2.
        print("In method 2 - Protocol A")
    }
}

class A : ProtocolA {
    func method1() {
        print("In method 1 - Class A")
    }

//  func method2(){
//      // It comes here, instead of class B method2.
//      print("In method 2 - Class A")
//  }
}

class B : A {
    func method2() {
        print("In method 2 - Class B")
    }
}

var b : B = B()
b.method2()

The problem is the runtime choose the function that was implemented based on the Type of variable.

Extension doesn't go in derived class in swift

1 Answers1