Question

Every day I always come across this dilemma – is it best practice to check for an undesired state at the start of a function and return straight away or, is it best practice to check for a desired condition and continue else return false.

I understand that there wont be a 1 fits all solution and that this is really a style issue but I am just interested in what other developers would typically do.

I always find my self being indecisive every time this situation comes up.

As an example (coded in php):

Check for the undesired condition first…

function myFunction($myVal)
{
    if ($myVal != 'desiredVal') {
        return false;
    }

    //Continue here with main function code

    return true;
}

Or, check for the desired condition first…

function myFunction($myVal)
{
    if ($myVal == 'desiredVal') {
        //continue here with main function code

        return true;
    }

    return false;
}

Answer 1

It’s largely a matter of style and both are correct. I find error checking at the top followed by the main method functionality to be cleaner and easier to follow.

The best advice would be to pick a style and be consistent with it.