Why does this method with an optional parameter not override the base class method?

Question

The result is "a", but I want it to be "b". I want to know why, and how I can call doTest without arguments to print "b".

class AA {
    func doTest() {
        print("a")
    }
}

class BB: AA {
    func doTest(_ different: Bool = true) {
        print("b")
    }
}

let bObjc = BB()
bObjc.doTest()

Answer 1

Class BB does not override the method from AA, that means two methods exist on BB:

func doTest() // inherited
func doTest(_ different: Bool = true) // declared

When you call

bObjc.doTest()

the compiler has to choose one of them. And it prefers method without parameter over the method with a default parameter.