The case against case

Chances are you have written a switch case statement or two. Aren’t they much ‘cleaner’ than a bunch of if else statements? Today i would like to convince you that using switch case, in modern php, is a bad practice.

Lets take a look at the following code snippet.

<?php
//test.php
declare(strict_types=1);

class One
{
public function __toString()
{
return '1';
}
}

function foo($value) { switch ($value) {
case '1':
echo "got 1 \n";
break;

default:
echo "did not get 1\n";
break;
}
}

foo(new One());
foo(1);
foo('1');

$php test.php got 1 got 1 got 1 As we can see, switch case checks if its value is equal rather than the same, it uses == instead of ===. This means switch case will juggle types, in order to see if the values it has are ‘equal’. Even the declare(strict_types=1) doesn’t change anything about that. Our code bases are filled with === checks, we use declare(strict_types=1) in our php 7+ projects. If possible we enforce both of those in our code standards. Yet, we still use switch and case, while very case is an equal check rather than a same check. Which means its a potential for bugs/ unexpected behavior. So, if you are using switch case, refactor it into an if/else statement like so: <?php //test.php declare(strict_types=1); class One { public function __toString() { return '1'; } } function foo($value)
{
if ($value === '1') { echo "got 1 \n"; } else { echo "did not get 1\n"; } } foo(new One()); foo(1); foo('1');  $ php test.php
did not get 1
did not get 1
got 1

And suddenly, we are checking that the input is actually the string ‘1’, rather than something that is roughly the same. Of course, this is a rather simple example, but any switch case statement can be changed into an if else that will not type juggle. Another benefit of this is that magic methods like __toString() will not be called, just in case, god forbid, those have side effects.

Maybe if we are lucky we’ll see strict switch statements in future php versions. But until that day, lets stay away from switch case.

Gert de Pagter
Software Engineer

My interests include software development, math and magic.