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). An object's __clone() method cannot be called directly.
$copy_of_object = clone $object;When an object is cloned, PHP 5 will perform a shallow copy of all of the object's properties. Any properties that are references to other variables will remain references.
void __clone ( void )Once the cloning is complete, if a __clone() method is defined, then the newly created object's __clone() method will be called, to allow any necessary properties that need to be changed.
Example #1 Cloning an object
<?php
class?SubObject
{
????static?$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
)
)PHP 7.0.0 introduced the possibility to access a member of a freshly cloned object in a single expression:
Example #2 Access member of freshly cloned object
<?php
$dateTime?=?new?DateTime();
echo?(clone?$dateTime)->format('Y');
?>The above example will output something similar to:
2016Comparing Objects →
? 1997–2017 The PHP Documentation GroupLicensed under the Creative Commons Attribution License v3.0 or later.
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