Is there a need to pass variable by reference in php5?

Question

With PHP5 using "copy on write" and passing by reference causing more of a performance penalty than a gain, why should I use pass-by-reference? Other than call-back functions that would return more than one value or classes who's attributes you want to be alterable without calling a set function later(bad practice, I know), is there a use for it that I am missing?

Answer 1

You use pass-by-reference when you want to modify the result and that's all there is to it.

Remember as well that in PHP objects are always pass-by-reference.

Personally I find PHP's system of copying values implicitly (I guess to defend against accidental modification) cumbersome and unintuitive but then again I started in strongly typed languages, which probably explains that. But I find it interesting that objects differ from PHP's normal operation and I take it as evidence that PHP"s implicit copying mechanism really isn't a good system.

Answer 2

A recursive function that fills an array? Remember writing something like that, once.

There's no point in having hundreds of copies of a partially filled array and copying, splicing and joining parts at every turn.

Answer 3

Even when passing objects there is a difference.

Try this example:

class Penguin { }

$a = new Penguin();

function one($a)
{
  $a = null;
}

function two(&$a)
{
  $a = null;
}

var_dump($a);
one($a);
var_dump($a);
two($a);
var_dump($a);

The result will be:

object(Penguin)#1 (0) {}
object(Penguin)#1 (0) {}
NULL

When you pass a variable containing a reference to an object by reference, you are able to modify the reference to the object.