PHP Reference Silliness

Posted on by Chris Warburton

Today I needed to pop arrays in a loop in PHP, starting with one and falling back to another when it runs out. A naive implementation might do this:

if (count($bar)) {
  $foo = array_pop($bar);
else {
  $foo = array_pop($baz);

However, I always cringe when I see code like this. Why branch on a whole statement when you could just branch on the expression you care about?

$foo = count($bar)? array_pop($bar) : array_pop($baz);

Of course, this is still redundant, since we’re calling array_pop twice. Let’s shrink the branch again:

$foo = array_pop(count($bar)? $bar : $foo);

Aaaaaaaand… PHP dies. It won’t let us pass-by-reference with a calculated expression like this ternary statement. Sad times. We can sometimes work around PHP’s stupid pass-by-reference crap using call_user_func, but not this time. However, we can call-by-reference on elements inside an array, and we can look up those elements using a calculated expression. This means we can swap $bar and $baz for $a = array($bar, $baz) and use the following:

$foo = array_pop($a[count($a[0]) > 0]);

In fact, while writing this up, I found another refactoring in the generation of $bar and $baz which lets me do away with their distinction by the time we get this far, so I can just array_merge them together and pop that until it’s empty :)