Override property observer

You can override the set and get part of the property and move your println there. This way Swift won't call the original code -- unless you call super.

class Foo {
    private var _something: Int!

    var something: Int! {
        get {
            return _something
        }
        set {
            _something = newValue
            println("vroom")
        }
    }
}

class Bar: Foo {
    override var something: Int! {
        get {
            return _something
        }
        set {
            _something = newValue
            println("toot toot")
        }
    }
}

That's not pretty, though.

Here's a better -- and simpler -- solution:

class Foo {
    var something: Int! {
        didSet {
            somethingWasSet()
        }
    }

    func somethingWasSet() {
        println("vroom")
    }
}

class Bar: Foo {
    override func somethingWasSet() {
        println("toot toot")
    }
}

Since there is no way to "override" the didSet, what remains is overriding a secondary function especially created for that purpose.

From the Swift documentation

The willSet and didSet observers of superclass properties are called when a property is set in a subclass initializer, after the superclass initializer has been called. They are not called while a class is setting its own properties, before the superclass initializer has been called.