Руководство по PHP
Пред. | Глава 18. Classes and Objects (PHP 4) | След.

# Comparing objects

In PHP 4, objects are compared in a very simple manner, namely: Two object instances are equal if they have the same attributes and values, and are instances of the same class. Similar rules are applied when comparing two objects using the identity operator (===).

If we were to execute the code in the example below:

Пример 18-1. Example of object comparison in PHP 4
`<?php function 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 { var $flag; function Flag($flag=true) { $this->flag = $flag; } } class SwitchableFlag extends Flag { function turnOn() { $this->flag = true; } function turnOff() { $this->flag = false; } } $o = new Flag(); $p = new Flag(false); $q = new Flag(); $r = new SwitchableFlag(); echo "Compare instances created with the same parameters\n"; compareObjects($o, $q); echo "\nCompare instances created with different parameters\n"; compareObjects($o, $p); echo "\nCompare an instance of a parent class with one from a subclass\n"; compareObjects($o, $r); ?>`
Результат выполнения данного примера:
    Compare instances created with the same parameters
    o1 == o2 : TRUE
    o1 != o2 : FALSE
    o1 === o2 : TRUE
    o1 !== o2 : FALSE

    Compare instances created with different parameters
    o1 == o2 : FALSE
    o1 != o2 : TRUE
    o1 === o2 : FALSE
    o1 !== o2 : TRUE

    Compare an instance of a parent class with one from a subclass
    o1 == o2 : FALSE
    o1 != o2 : TRUE
    o1 === o2 : FALSE
    o1 !== o2 : TRUE

Which is the output we will expect to obtain given the comparison rules above. Only instances with the same values for their attributes and from the same class are considered equal and identical.

Even in the cases where we have object composition, the same comparison rules apply. In the example below we create a container class that stores an associative array of Flag objects.

Пример 18-2. Compound object comparisons in PHP 4
`<?php class FlagSet { var $set; function FlagSet($flagArr = array()) { $this->set = $flagArr; } function addFlag($name, $flag) { $this->set[$name] = $flag; } function removeFlag($name) { if (array_key_exists($name, $this->set)) { unset($this->set[$name]); } } } $u = new FlagSet(); $u->addFlag('flag1', $o); $u->addFlag('flag2', $p); $v = new FlagSet(array('flag1'=>$q, 'flag2'=>$p)); $w = new FlagSet(array('flag1'=>$q)); echo "\nComposite objects u(o,p) and v(q,p)\n"; compareObjects($u, $v); echo "\nu(o,p) and w(q)\n"; compareObjects($u, $w); ?>`
Результат выполнения данного примера:
    Composite objects u(o,p) and v(q,p)
    o1 == o2 : TRUE
    o1 != o2 : FALSE
    o1 === o2 : TRUE
    o1 !== o2 : FALSE

    u(o,p) and w(q)
    o1 == o2 : FALSE
    o1 != o2 : TRUE
    o1 === o2 : FALSE
    o1 !== o2 : TRUE

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References inside the constructor | Уровень выше | Классы и объекты (PHP 5)