Comparing Objects

- « Object Cloning

- Late Static Bindings »

- PHP Manual
- Classes and Objects
- Comparing Objects

## Comparing Objects

When using the comparison operator (`==`), object variables are compared in a simple manner, namely: Two object instances are equal if they have the same attributes and values (values are compared with `==`), and are instances of the same class.

When using the identity operator (`===`), object variables are identical if and only if they refer to the same instance of the same class.

An example will clarify these rules.

Example #1 Example of object comparison

    <?phpfunction bool2str($bool){    if ($bool === false) {        return 'FALSE';    } else {        return 'TRUE';    }}function compareObjects(&$o1, &$o2){    echo 'o1 == o2 : ' . bool2str($o1 == $o2) . "\n";    echo 'o1 != o2 : ' . bool2str($o1 != $o2) . "\n";    echo 'o1 === o2 : ' . bool2str($o1 === $o2) . "\n";    echo 'o1 !== o2 : ' . bool2str($o1 !== $o2) . "\n";}class Flag{    public $flag;    function __construct($flag = true) {        $this->flag = $flag;    }}class OtherFlag{    public $flag;    function __construct($flag = true) {        $this->flag = $flag;    }}$o = new Flag();$p = new Flag();$q = $o;$r = new OtherFlag();echo "Two instances of the same class\n";compareObjects($o, $p);echo "\nTwo references to the same instance\n";compareObjects($o, $q);echo "\nInstances of two different classes\n";compareObjects($o, $r);?>

The above example will output:

    Two instances of the same class
    o1 == o2 : TRUE
    o1 != o2 : FALSE
    o1 === o2 : FALSE
    o1 !== o2 : TRUE

    Two references to the same instance
    o1 == o2 : TRUE
    o1 != o2 : FALSE
    o1 === o2 : TRUE
    o1 !== o2 : FALSE

    Instances of two different classes
    o1 == o2 : FALSE
    o1 != o2 : TRUE
    o1 === o2 : FALSE
    o1 !== o2 : TRUE

> Note:

> Extensions can define own rules for their objects comparison (`==`).