Be careful about the switch statement in PHP

Could you find the difference in results between these two codes?

function getStatusByCode($code)
{   
    $status = '';

    switch ($code) {
        case 0:
            $status = 'OK';
            break;

        case 1: 
            $status = 'WARNING';
            break;

        default:
            $status = 'UNDEFINED';
            break;
    }    

    return $status;
}

var_dump(getStatusByCode(null));

and

function getStatusByCode($code)
{   
    $status = '';

    if ($code === 0) {
        $status = 'OK';
    } elseif ($code === 1) {
        $status = 'WARNING';
    } else {
        $status = 'UNDEFINED';
    }

    return $status;
}

var_dump(getStatusByCode(null));

So have you found it?

In the first case with the switch, the method returns OK.
In the second case, the method returns UNDEFINED.

But why this difference?

The first code with the switch comes from a legacy code base: no type hinting on the arguments, no return from the function. And this code was the cause of a small bug, because switch uses loose comparison: using == instead of === to compare values.

And in PHP with the loose comparison, null equals 0.

So be careful when you have a sequence of if / elseif / else, switching to switch can have an impact on the expected behavior.

So what to do?

If you follow me a little, I recommend that you use the strict comparison with === most often (if not all the time).

So if you want to keep this behavior, some ideas:

You leave your sequence of if / elseif / else
You reinforce your function parameters with types to ensure you never have an unwanted value (if that's the case)

function getStatusByCode(int $code)
{   
    $status = '';

    switch ($code) {
        case 0:
            $status = 'OK';
            break;

        case 1: 
            $status = 'WARNING';
            break;

        default:
            $status = 'UNDEFINED';
            break;
    }    

    return $status;
}

var_dump(getStatusByCode(null));

/* Result : Fatal error: Uncaught TypeError: 
 * Argument 1 passed to getStatusByCode() must be of the type int, null given
 */

You are using match available since PHP 8 which uses strict comparison 👍

function getStatusByCode($code)
{
    return match($code) {
        0 => 'OK',
        1 => 'WARNING',
        default => 'UNDEFINED',
    };
}

Thank you for reading, and let's stay in touch !

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Jimmy Klein @klnjmm