Is returning early from a function more elegant than an if statement?

Question

Myself and a colleague have a dispute about which of the following is more elegant. I won't say who's who, so it is impartial. Which is more elegant?

public function set hitZone(target:DisplayObject):void
{
    if(_hitZone != target)
    {
        _hitZone.removeEventListener(MouseEvent.ROLL_OVER, onBtOver);
        _hitZone.removeEventListener(MouseEvent.ROLL_OUT, onBtOut);
        _hitZone.removeEventListener(MouseEvent.MOUSE_DOWN, onBtDown);

        _hitZone = target;

        _hitZone.addEventListener(MouseEvent.ROLL_OVER, onBtOver, false, 0, true);
        _hitZone.addEventListener(MouseEvent.ROLL_OUT, onBtOut, false, 0, true);
        _hitZone.addEventListener(MouseEvent.MOUSE_DOWN, onBtDown, false, 0, true);
    }
}

...or...

public function set hitZone(target:DisplayObject):void
{
    if(_hitZone == target) return;

    _hitZone.removeEventListener(MouseEvent.ROLL_OVER, onBtOver);
    _hitZone.removeEventListener(MouseEvent.ROLL_OUT, onBtOut);
    _hitZone.removeEventListener(MouseEvent.MOUSE_DOWN, onBtDown);

    _hitZone = target;

    _hitZone.addEventListener(MouseEvent.ROLL_OVER, onBtOver, false, 0, true);
    _hitZone.addEventListener(MouseEvent.ROLL_OUT, onBtOut, false, 0, true);
    _hitZone.addEventListener(MouseEvent.MOUSE_DOWN, onBtDown, false, 0, true);
}

Answer 1

This is one of those cases where it's ok to break the rules (i.e. best practices). In general you want to have as few return points in a function as possible. The practical reason for this is that it simplifies your reading of the code, since you can just always assume that each and every function will take its arguments, do its logic, and return its result. Putting in extra returns for various cases tends to complicate the logic and increase the amount of time necessary to read and fully grok the code. Once your code reaches the maintenance stage then multiple returns can have a huge impact on the productivity of new programmers as they try to decipher the logic (its especially bad when comments are sparse and the code unclear). The problem grows exponentially with respect to the length of the function.

So then why in this case does everyone prefer option 2? It's because you're are setting up a contract that the function enforces through validating incoming data, or other invariants that might need to be checked. The prettiest syntax for constructing the validation is the check each condition, returning immediately if the condition fails validity. That way you don't have to maintain some kind of isValid boolean through all of your checks.

To sum things up: we're really looking at how to write validation code and not general logic; option 2 is better for validation code.