Passing by Reference

You can pass a variable by reference to a function so the function can modify the variable. The syntax is as follows:

<?phpfunction foo(&$var){    $var++;}$a=5;foo($a);// $a is 6 here?>

Note: There is no reference sign on a function call - only on function definitions. Function definitions alone are enough to correctly pass the argument by reference.

The following things can be passed by reference:

No other expressions should be passed by reference, as the result is undefined. For example, the following examples of passing by reference are invalid:

<?phpfunction foo(&$var){    $var++;}function bar() // Note the missing &{    $a = 5;    return $a;}foo(bar()); // Produces a noticefoo($a = 5); // Expression, not variablefoo(5); // Produces fatal errorclass Foobar{}foo(new Foobar()) // Produces a notice as of PHP 7.0.7                  // Notice: Only variables should be passed by reference?>