php - Only variables can be passed by reference

Question

I had the bright idea of using a custom error handler which led me down a rabbit hole.

Following code gives (with and without custom error handler): Fatal error: Only variables can be passed by reference

function foo(){
    $b=array_pop(array("a","b","c"));
    return $b;
}
print_r(foo());

Following code gives (only with a custom error handler): (2048) Only variables should be passed by reference

function foo(){
    $a=explode( '/' , 'a/b/c');
    $c=array_pop(array_slice($a,-2,1));
    return $c;
}
print_r(foo());

The second one worries me since I have a lot of 'compact' code. So, I either ditch the bright idea of using a custom error handler (to improve my logging module) or expand all my code.

Anyone with better ideas? Also, WTF?

UPDATE:

Thanks to the answers I've learnt something about how php does error handling. The confusion of E_ALL not including E_STRICT (php 5) is not cool.

On top of all this, creating your own custom error handler enables E_STRICT by default and thats where problems start.

The moral of the story is to use your own error handler to catch them ALL and use the error constants (E_STRICT, E_USER_WARNING, E_USER_ERROR, etc.) to do your filtering.

As for the 'memory corruption issue' with variable references and certain functions, what can I say? Doubly uncool. I'll (which doesn't mean you should) ignore E_STRICT in my error handler and life goes on.

Answer 1

array_pop() tries to change that value which is passed as parameter. Now in your second example this is the return value from array_slice(). In engine terms this is a "temporary value" and such a value can't be passed by references. what you need is a temporary variable:

function foo(){
    $a=explode( '/' , 'a/b/c');
    $b=array_slice($a,-2,1);
    $c=array_pop($b);
    return $c;
}
print_r(foo());

Then a reference to $b can be passed to array_pop(). See http://php.net/references for more details on references.