Assignment by Reference Operator in PHP

1. Use the =& Operator to Create a Non-Existent Variable in PHP
2. Use the =& Operator to Point More Than One Variable to the Same Value (Memory Location) in PHP
3. Use the =& Operator to Link More Than One Variable in PHP
4. Use the =& Operator to Unlink More Than One Variable in PHP

This article demonstrates creating a non-existent variable, pointing more than one variable to the same value, linking multiple variables, and unlinking multiple variables using the assignment by reference or the =& operator or in PHP.

Use the =& Operator to Create a Non-Existent Variable in PHP

We will create an array and use the assignment by reference operator to create an array variable without initially declaring the variable.

<?php
    $test = array();
    $test1 =& $test['z'];
    var_dump($test);
?>

Output:

array(1) {
	["z"]=>
	&NULL
}

Use the =& Operator to Point More Than One Variable to the Same Value (Memory Location) in PHP

We will create a variable, assign a value to it, and then use the assignment by reference operator to make other variables point to the same memory location as the first variable.

<?php
    $firstValue=100;
    $secondValue =& $firstValue;
    echo "First Value=".$firstValue."<br>";
    echo "Second Value=". $secondValue."<br>";
    $firstValue = 45000;
    echo "After changing the value of firstValue, secondValue will reflect the firstValue  because of =&","<br>";
    echo "First Value=". $firstValue."<br>";
    echo "Second Value=". $secondValue;
?>

Output:

First Value=100
Second Value=100

After changing the value of firstValue, secondValue will reflect the firstValue  because of =&

First Value=45000
Second Value=45000

Use the =& Operator to Link More Than One Variable in PHP

We will create a variable, assign a value to it, and then use the assignment by reference operator to link other variables to the initial variable. They all point to the initial variable value.

<?php
    $second = 50;
    $first =& $second;
    $third =& $second;
    $fourth =& $first;
    $fifth =& $third;

    // $first, $second, $third, $fourth, and $fifth now all point to the same data, interchangeably

    //should print 50
    echo $fifth;
?>

Output:

50

Use the =& Operator to Unlink More Than One Variable in PHP

We will create two variables and assign values to them. Then use the assignment by reference operator to link and unlink other variables.

The variables point to different values.

<?php
    $second = 50;
    $sixth = 70;
    $first =& $second;
    $third =& $second;
    $fourth =& $first;
    $fifth =& $third;

    // $first, $second, $third, $fourth, and $fifth now all point to the same data, interchangeably

    //unlink $fourth from our link, now $fourth is linked to $sixth and not $third
    $fourth = $sixth;

    echo $fourth;
?>

Output:

70