Object Cloning

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).

$copy_of_object = clone $object;

When an object is cloned, PHP will perform a shallow copy of all of the object's properties. Any properties that are references to other variables will remain references.

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.

<?phpclass 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);?>

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
        )

)

It is possible to access a member of a freshly cloned object in a single expression:

<?php$dateTime = new DateTime();echo (clone $dateTime)->format('Y');?>

2016