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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<sect1 xml:id="language.oop5.object-comparison" xmlns="http://docbook.org/ns/docbook">
<title>Comparing Objects</title>
<para>
When using the comparison operator (<literal>==</literal>),
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 <literal>==</literal>), and are
instances of the same class.
</para>
<para>
When using the identity operator (<literal>===</literal>),
object variables are identical if and only if they refer to the same
instance of the same class.
</para>
<para>
An example will clarify these rules.
<example>
<title>Example of object comparison</title>
<programlisting role="php">
<![CDATA[
<?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
{
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);
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
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
]]>
</screen>
</example>
</para>
<note>
<para>
Extensions can define own rules for their objects comparison
(<literal>==</literal>).
</para>
</note>
</sect1>
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