best way make default param = a variable?

Question

I have a variable, and a function for brevity lets consider it looks like this:

private function applyDiscount (value:Number):Number
{
return value*_discount; //_discount defined somewhere else
}

OK thats all fine and dandy but say I want to be able to call that function and be able to pass my own discount, but still use the _discount as a default.

I CAN do this:

private function applyDiscount (value:Number, discount:Number = 50):Number
    {
    return value*discount;
    }

This will make discount default to 50 but I don't know it at authortime so I need to do this but its not allowed in Flex.

private function applyDiscount (value:Number, discount:Number = _discount):Number
    {
    return value*discount;
    }

So my question is, what is the best way to achieve the same as the last example in Flex?

Thanks.

Answer 1

Maybe have the discount exposed as a public property so you can set it separately to the method call. e.g

public function get discount():Number{ 
    return _discount; 
} 

public function set discount(param:Number):void { 
    _discount = param; 
}

private function applyDiscount (value:Number):Number
{
    return value*_discount; //_discount defined somewhere else
}

The additional function looked goofy in the comments so I have added it here... Basically you could make the discount an optional parameter.

function applyDiscount(value:Number, ... rest):void {
    if(rest.length > 0) {
        return value*rest[0];
    } else {
        return value*_discount; //_discount defined somewhere else
    }
}

applyDiscount(100, 10); // 10 discount...
applyDiscount(100); // default discount...

Answer 2

private function applyDiscount(value: Number, discount : Number = Number.POSITIVE_INFINITY){
   if(discount == Number.POSITIVE_INFINITY) discount = _discount;
    return value*discount;
}