Question

PHP has some great functions (like array_walk) that allow you to process each element in an array. They’re generally set up so you specify the array you want processed as the first parameter and a callback function to apply to each element as the second. These functions return booleans indicating success, not a copy of the modified array as you might expect. If you want the array to be modified, you have to pass the array in by reference like array_walk(&$my_array, 'my_callback');

However, in PHP 5.3 and above, if you pass by reference to function call you get a E_DEPRECATED error.

Does anyone know (if there exists) a correct way to use these functions to modify arrays without triggering the errors and without explicitly suppressing them? Are there newer alternatives to these old array processing functions.

Answer 1

Values are passed by reference implicitly in PHP >= 5.3 as determined by the function definition.

Function definition for array_walk():

bool array_walk ( array &$array , callable $funcname [, mixed $userdata = NULL ] )

Note &$array. As such, you do not need to explicitly pass the array by reference in the function call in PHP >= 5.3.

array_walk($my_array, 'my_callback');

However, you will need to ensure that the callback accepts it’s value by reference accordingly (as demonstrated by nickb).

Also take a look at PHP 5.4 Call-time pass-by-reference – Easy fix available?