Overriding parent methods with contravariant arguments

Question

Basically, I want to override a parent class with different arguments. For example:

class Hold<T> {
    public var value:T;
    public function new(value:T) {
        set(value);
    }
    public function set(value:T) {
        this.value = value;
    }
}

Then override that class, something like:

class HoldMore extends Hold<T> {
    public var value2:T;
    public function new(value:T, value2:T) {
        super(value);
        set(value, value2);
    }
    override public function set(value:T, value2:T) {
        this.value = value;
        this.value2 = value2;
    }
}

Obviously this will return an error, Field set overloads parent class with different or incomplete type. Is there a way around this? I tried using a public dynamic function, and then setting set in the new() function, but that gave a very similar error. Any thoughts?

Answer 1

This is just a complement to @stroncium's answer, which is totally correct.

Here is an example how it could look like:

class Hold<T> {
    public var value:T;
    public function new(value:T) {
        set(value);
    }
    public function set(value:T) {
        this.value = value;
    }
}

class HoldMore<T> extends Hold<T> {
    public var value2:T;
    public function new(value:T, value2:T) {
        super(value);
        setBoth(value, value2);
    }
    // you cannot override "set" with a different signature
    public function setBoth(value:T, value2:T) {
        this.value = value;
        this.value2 = value2;
    }
}

alternatively, you could use an array as parameter or a dynamic object holding multiple values in order to "set" them using the same method, but you loose some of the compiler's type checking.

Answer 2

If you wrote the base class you could add an optional argument to it, this would be a workaround though, not directly what you want to do.