Passing by Reference

You can pass variable to function by reference, so that function could modify its arguments. The syntax is as follows:

<?php
function foo (&$var)
{
    $var++;
}

$a=5;
foo ($a);
// $a is 6 here
?>

Following things can be passed by reference:

• Variable, i.e. foo($a)

• New statement, i.e. foo(new foobar())

• Reference, returned from a function, i.e.:

  <?php function &bar() { $a = 5; return $a; } foo(bar()); ?>

  See also explanations about returning by reference.

Any other expression should not be passed by reference, as the result is undefined. For example, the following examples of passing by reference are invalid:

<?php
function bar() // Note the missing &
{
    $a = 5;
    return $a;
}
foo(bar());

foo($a = 5) // Expression, not variable
foo(5) // Constant, not variable
?>