Passing By Reference¶

When calling a method, or returning from it, data may be passed by value or by reference.

By reference, a reference to the the data is passed: any modification on that value inside the method will be reflected in the original value.

This is the alternative way of passing data to methods: the default way is to use by value, which copies the data.

Passing by reference is the default behavior with object. Otherwise, it needs to be declared with the & operator, in the function signature.

Returned value are passed back to the calling context with the same rule than for parameters.

<?php

$a = 0;
foo($a);  // displays 1
print $a; // displays 1

function foo(&$a) {
    ++$a;
    echo $a;
}

?>