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<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.4 $ -->
<sect1 id="language.oop5.cloning">
<title>Object cloning</title>
<para>
Creating a copy of an object with fully replicated properties is not
always the wanted behavior. A good example of the need for copy
constructors, is if you have an object which represents a GTK window and the
object holds the resource of this GTK window, when you create a duplicate
you might want to create a new window with the same properties and have the
new object hold the resource of the new window. Another example is if your
object holds a reference to another object which it uses and when you
replicate the parent object you want to create a new instance of this other
object so that the replica has its own separate copy.
</para>
<para>
An object copy is created by using the clone keyword (which calls the
object's __clone() method if possible). An object's __clone() method
cannot be called directly.
</para>
<informalexample>
<programlisting>
<![CDATA[
$copy_of_object = clone $object;
]]>
</programlisting>
</informalexample>
<para>
When an object is cloned, PHP 5 will perform a shallow copy of all of the
object's properties. Any properties that are references to other variables,
will remain references. If a __clone() method is defined, then the newly
created object's __clone() method will be called, to allow any necessary
properties that need to be changed.
</para>
<example>
<title>Cloning an object</title>
<programlisting role="php">
<![CDATA[
<?php
class SubObject
{
static $instances = 0;
public $instance;
public function __construct() {
$this->instance = ++self::$instances;
}
public function __clone() {
$this->instance = ++self::$instances;
}
}
class MyCloneable
{
public $object1;
public $object2;
function __clone()
{
// Force a copy of this->object, otherwise
// it will point to same object.
$this->object1 = clone($this->object1);
}
}
$obj = new MyCloneable();
$obj->object1 = new SubObject();
$obj->object2 = new SubObject();
$obj2 = clone $obj;
print("Original Object:\n");
print_r($obj);
print("Cloned Object:\n");
print_r($obj2);
?>
]]>
</programlisting>
&example.outputs;
<screen role="php">
<![CDATA[
Original Object:
MyCloneable Object
(
[object1] => SubObject Object
(
[instance] => 1
)
[object2] => SubObject Object
(
[instance] => 2
)
)
Cloned Object:
MyCloneable Object
(
[object1] => SubObject Object
(
[instance] => 3
)
[object2] => SubObject Object
(
[instance] => 2
)
)
]]>
</screen>
</example>
</sect1>
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vim600: syn=xml fen fdm=syntax fdl=2 si
vim: et tw=78 syn=sgml
vi: ts=1 sw=1
-->
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