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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@331094 c90b9560-bf6c-de11-be94-00142212c4b1
130 lines
2.9 KiB
XML
130 lines
2.9 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<sect1 xml:id="language.oop5.object-comparison" xmlns="http://docbook.org/ns/docbook">
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<title>Comparing Objects</title>
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<para>
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In PHP 5, object comparison is more complicated than in PHP 4 and more
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in accordance to what one will expect from an Object Oriented Language
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(not that PHP 5 is such a language).
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</para>
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<para>
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When using the comparison operator (<literal>==</literal>),
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object variables are compared in a simple manner, namely: Two object
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instances are equal if they have the same attributes and values, and are
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instances of the same class.
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</para>
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<para>
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On the other hand, when using the identity operator (<literal>===</literal>),
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object variables are identical if and only if they refer to the same
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instance of the same class.
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</para>
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<para>
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An example will clarify these rules.
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<example>
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<title>Example of object comparison in PHP 5</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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function bool2str($bool)
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{
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if ($bool === false) {
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return 'FALSE';
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} else {
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return 'TRUE';
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}
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}
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function compareObjects(&$o1, &$o2)
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{
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echo 'o1 == o2 : ' . bool2str($o1 == $o2) . "\n";
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echo 'o1 != o2 : ' . bool2str($o1 != $o2) . "\n";
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echo 'o1 === o2 : ' . bool2str($o1 === $o2) . "\n";
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echo 'o1 !== o2 : ' . bool2str($o1 !== $o2) . "\n";
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}
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class Flag
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{
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public $flag;
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function Flag($flag = true) {
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$this->flag = $flag;
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}
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}
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class OtherFlag
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{
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public $flag;
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function OtherFlag($flag = true) {
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$this->flag = $flag;
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}
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}
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$o = new Flag();
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$p = new Flag();
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$q = $o;
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$r = new OtherFlag();
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echo "Two instances of the same class\n";
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compareObjects($o, $p);
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echo "\nTwo references to the same instance\n";
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compareObjects($o, $q);
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echo "\nInstances of two different classes\n";
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compareObjects($o, $r);
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?>
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]]>
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</programlisting>
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&example.outputs;
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<screen>
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<![CDATA[
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Two instances of the same class
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o1 == o2 : TRUE
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o1 != o2 : FALSE
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o1 === o2 : FALSE
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o1 !== o2 : TRUE
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Two references to the same instance
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o1 == o2 : TRUE
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o1 != o2 : FALSE
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o1 === o2 : TRUE
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o1 !== o2 : FALSE
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Instances of two different classes
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o1 == o2 : FALSE
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o1 != o2 : TRUE
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o1 === o2 : FALSE
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o1 !== o2 : TRUE
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]]>
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</screen>
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</example>
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</para>
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<note>
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<para>
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Extensions can define own rules for their objects comparison
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(<literal>==</literal>).
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</para>
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</note>
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</sect1>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"~/.phpdoc/manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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