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https://github.com/sigmasternchen/php-doc-en
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5c05004b29
git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@315146 c90b9560-bf6c-de11-be94-00142212c4b1
87 lines
2 KiB
XML
87 lines
2 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<sect1 xml:id="language.oop5.references" xmlns="http://docbook.org/ns/docbook">
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<title>Objects and references</title>
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<para>
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One of the key-points of PHP 5 OOP that is often mentioned is that
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"objects are passed by references by default". This is not completely true.
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This section rectifies that general thought using some examples.
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</para>
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<para>
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A PHP reference is an alias, which allows two different variables to write
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to the same value. As of PHP 5, an object variable doesn't contain the object
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itself as value anymore. It only contains an object identifier which allows
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object accessors to find the actual object. When an object is sent by
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argument, returned or assigned to another variable, the different variables
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are not aliases: they hold a copy of the identifier, which points to the same
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object.
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</para>
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<example>
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<title>References and Objects</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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class A {
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public $foo = 1;
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}
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$a = new A;
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$b = $a; // $a and $b are copies of the same identifier
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// ($a) = ($b) = <id>
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$b->foo = 2;
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echo $a->foo."\n";
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$c = new A;
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$d = &$c; // $c and $d are references
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// ($c,$d) = <id>
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$d->foo = 2;
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echo $c->foo."\n";
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$e = new A;
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function foo($obj) {
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// ($obj) = ($e) = <id>
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$obj->foo = 2;
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}
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foo($e);
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echo $e->foo."\n";
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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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2
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2
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2
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]]>
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</screen>
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</example>
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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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