Object Cloning

Examples:

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.

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.

$copy_of_object = clone $object;

Cloning an object

Once the cloning is complete, 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.

<?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);
 
?>

The above example will output:

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
        )

)

Links:

http://php.net/manual/en/language.oop5.cloning.php

doc_php

2025-01-10 15:47:30

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