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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@224288 c90b9560-bf6c-de11-be94-00142212c4b1
147 lines
3.2 KiB
XML
147 lines
3.2 KiB
XML
<?xml version="1.0" encoding="iso-8859-1"?>
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<!-- $Revision: 1.5 $ -->
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<sect1 id="language.oop5.cloning">
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<title>Object cloning</title>
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<para>
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Creating a copy of an object with fully replicated properties is not
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always the wanted behavior. A good example of the need for copy
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constructors, is if you have an object which represents a GTK window and the
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object holds the resource of this GTK window, when you create a duplicate
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you might want to create a new window with the same properties and have the
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new object hold the resource of the new window. Another example is if your
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object holds a reference to another object which it uses and when you
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replicate the parent object you want to create a new instance of this other
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object so that the replica has its own separate copy.
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</para>
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<para>
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An object copy is created by using the clone keyword (which calls the
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object's __clone() method if possible). An object's __clone() method
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cannot be called directly.
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</para>
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<informalexample>
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<programlisting>
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<![CDATA[
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$copy_of_object = clone $object;
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]]>
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</programlisting>
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</informalexample>
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<para>
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When an object is cloned, PHP 5 will perform a shallow copy of all of the
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object's properties. Any properties that are references to other variables,
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will remain references. If a __clone() method is defined, then the newly
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created object's __clone() method will be called, to allow any necessary
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properties that need to be changed.
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</para>
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<example>
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<title>Cloning an object</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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class SubObject
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{
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static $instances = 0;
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public $instance;
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public function __construct() {
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$this->instance = ++self::$instances;
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}
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public function __clone() {
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$this->instance = ++self::$instances;
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}
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}
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class MyCloneable
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{
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public $object1;
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public $object2;
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function __clone()
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{
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// Force a copy of this->object, otherwise
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// it will point to same object.
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$this->object1 = clone $this->object1;
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}
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}
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$obj = new MyCloneable();
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$obj->object1 = new SubObject();
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$obj->object2 = new SubObject();
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$obj2 = clone $obj;
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print("Original Object:\n");
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print_r($obj);
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print("Cloned Object:\n");
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print_r($obj2);
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?>
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]]>
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</programlisting>
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&example.outputs;
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<screen role="php">
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<![CDATA[
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Original Object:
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MyCloneable Object
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(
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[object1] => SubObject Object
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(
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[instance] => 1
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)
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[object2] => SubObject Object
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(
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[instance] => 2
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)
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)
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Cloned Object:
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MyCloneable Object
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(
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[object1] => SubObject Object
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(
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[instance] => 3
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)
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[object2] => SubObject Object
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(
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[instance] => 2
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)
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)
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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:"../../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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