Variables in PHP: Assign by reference 

<?php
$foo = 'Bob';              // Assign the value 'Bob' to $foo
$bar = &$foo;              // Reference $foo via $bar.
$bar = "My name is $bar";  // Alter $bar...
echo $bar;
echo $foo;                 // $foo is altered too.
?>
The code snippet outputs 'My name is Bob' twice.
  • This means that the new variable simply references (in other words, "becomes an alias for" or "points to") the original variable.
  • Changes to the new variable affect the original, and vice versa.
  • To assign by reference, simply prepend an ampersand (&) to the beginning of the variable which is being assigned (the source variable).
  • Only named variables may be assigned by reference. 
    <?php
$foo = 25;
$bar = &$foo;      // This is a valid assignment.
$bar = &(24 * 7);  // Invalid; references an unnamed expression.

function test()
{
   return 25;
}

$bar = &test();    // Invalid.
?>

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