It appears that in PHP objects are passed by reference. Even assignment operators do not appear to be creating a copy of the Object.
Here's a simple, contrived proof:
<?php
class A {
public $b;
}
function set_b($obj) { $obj->b = "after"; }
$a = new A();
$a->b = "before";
$c = $a; //i would especially expect this to create a copy.
set_b($a);
print $a->b; //i would expect this to show 'before'
print $c->b; //i would ESPECIALLY expect this to show 'before'
?>
In both print cases I am getting 'after'
So, how do I pass $a to set_b() by value, not by reference?
This question is related to
php
copy
clone
shallow-copy
In this example we will create iPhone class and make exact copy from it by cloning
class iPhone {
public $name;
public $email;
public function __construct($n, $e) {
$this->name = $n;
$this->email = $e;
}
}
$main = new iPhone('Dark', '[email protected]');
$copy = clone $main;
// if you want to print both objects, just write this
echo "<pre>"; print_r($main); echo "</pre>";
echo "<pre>"; print_r($copy); echo "</pre>";
I was doing some testing and got this:
class A {
public $property;
}
function set_property($obj) {
$obj->property = "after";
var_dump($obj);
}
$a = new A();
$a->property = "before";
// Creates a new Object from $a. Like "new A();"
$b = new $a;
// Makes a Copy of var $a, not referenced.
$c = clone $a;
set_property($a);
// object(A)#1 (1) { ["property"]=> string(5) "after" }
var_dump($a); // Because function set_property get by reference
// object(A)#1 (1) { ["property"]=> string(5) "after" }
var_dump($b);
// object(A)#2 (1) { ["property"]=> NULL }
var_dump($c);
// object(A)#3 (1) { ["property"]=> string(6) "before" }
// Now creates a new obj A and passes to the function by clone (will copied)
$d = new A();
$d->property = "before";
set_property(clone $d); // A new variable was created from $d, and not made a reference
// object(A)#5 (1) { ["property"]=> string(5) "after" }
var_dump($d);
// object(A)#4 (1) { ["property"]=> string(6) "before" }
?>
According to previous comment, if you have another object as a member variable, do following:
class MyClass {
private $someObject;
public function __construct() {
$this->someObject = new SomeClass();
}
public function __clone() {
$this->someObject = clone $this->someObject;
}
}
Now you can do cloning:
$bar = new MyClass();
$foo = clone $bar;
The answers are commonly found in Java books.
cloning: If you don't override clone method, the default behavior is shallow copy. If your objects have only primitive member variables, it's totally ok. But in a typeless language with another object as member variables, it's a headache.
serialization/deserialization
$new_object = unserialize(serialize($your_object))
This achieves deep copy with a heavy cost depending on the complexity of the object.
According to the docs (http://ca3.php.net/language.oop5.cloning):
$a = clone $b;
In this example we will create iPhone class and make exact copy from it by cloning
class iPhone {
public $name;
public $email;
public function __construct($n, $e) {
$this->name = $n;
$this->email = $e;
}
}
$main = new iPhone('Dark', '[email protected]');
$copy = clone $main;
// if you want to print both objects, just write this
echo "<pre>"; print_r($main); echo "</pre>";
echo "<pre>"; print_r($copy); echo "</pre>";
This code help clone methods
class Foo{
private $run=10;
public $foo=array(2,array(2,8));
public function hoo(){return 5;}
public function __clone(){
$this->boo=function(){$this->hoo();};
}
}
$obj=new Foo;
$news= clone $obj;
var_dump($news->hoo());
According to previous comment, if you have another object as a member variable, do following:
class MyClass {
private $someObject;
public function __construct() {
$this->someObject = new SomeClass();
}
public function __clone() {
$this->someObject = clone $this->someObject;
}
}
Now you can do cloning:
$bar = new MyClass();
$foo = clone $bar;
Just to clarify PHP uses copy on write, so basically everything is a reference until you modify it, but for objects you need to use clone and the __clone() magic method like in the accepted answer.
According to previous comment, if you have another object as a member variable, do following:
class MyClass {
private $someObject;
public function __construct() {
$this->someObject = new SomeClass();
}
public function __clone() {
$this->someObject = clone $this->someObject;
}
}
Now you can do cloning:
$bar = new MyClass();
$foo = clone $bar;
I was doing some testing and got this:
class A {
public $property;
}
function set_property($obj) {
$obj->property = "after";
var_dump($obj);
}
$a = new A();
$a->property = "before";
// Creates a new Object from $a. Like "new A();"
$b = new $a;
// Makes a Copy of var $a, not referenced.
$c = clone $a;
set_property($a);
// object(A)#1 (1) { ["property"]=> string(5) "after" }
var_dump($a); // Because function set_property get by reference
// object(A)#1 (1) { ["property"]=> string(5) "after" }
var_dump($b);
// object(A)#2 (1) { ["property"]=> NULL }
var_dump($c);
// object(A)#3 (1) { ["property"]=> string(6) "before" }
// Now creates a new obj A and passes to the function by clone (will copied)
$d = new A();
$d->property = "before";
set_property(clone $d); // A new variable was created from $d, and not made a reference
// object(A)#5 (1) { ["property"]=> string(5) "after" }
var_dump($d);
// object(A)#4 (1) { ["property"]=> string(6) "before" }
?>
The answers are commonly found in Java books.
cloning: If you don't override clone method, the default behavior is shallow copy. If your objects have only primitive member variables, it's totally ok. But in a typeless language with another object as member variables, it's a headache.
serialization/deserialization
$new_object = unserialize(serialize($your_object))
This achieves deep copy with a heavy cost depending on the complexity of the object.
This code help clone methods
class Foo{
private $run=10;
public $foo=array(2,array(2,8));
public function hoo(){return 5;}
public function __clone(){
$this->boo=function(){$this->hoo();};
}
}
$obj=new Foo;
$news= clone $obj;
var_dump($news->hoo());
According to previous comment, if you have another object as a member variable, do following:
class MyClass {
private $someObject;
public function __construct() {
$this->someObject = new SomeClass();
}
public function __clone() {
$this->someObject = clone $this->someObject;
}
}
Now you can do cloning:
$bar = new MyClass();
$foo = clone $bar;
According to the docs (http://ca3.php.net/language.oop5.cloning):
$a = clone $b;
The answers are commonly found in Java books.
cloning: If you don't override clone method, the default behavior is shallow copy. If your objects have only primitive member variables, it's totally ok. But in a typeless language with another object as member variables, it's a headache.
serialization/deserialization
$new_object = unserialize(serialize($your_object))
This achieves deep copy with a heavy cost depending on the complexity of the object.
If you want to fully copy properties of an object in a different instance, you may want to use this technique:
Serialize it to JSON and then de-serialize it back to Object.
The answers are commonly found in Java books.
cloning: If you don't override clone method, the default behavior is shallow copy. If your objects have only primitive member variables, it's totally ok. But in a typeless language with another object as member variables, it's a headache.
serialization/deserialization
$new_object = unserialize(serialize($your_object))
This achieves deep copy with a heavy cost depending on the complexity of the object.
According to the docs (http://ca3.php.net/language.oop5.cloning):
$a = clone $b;
If you want to fully copy properties of an object in a different instance, you may want to use this technique:
Serialize it to JSON and then de-serialize it back to Object.
Just to clarify PHP uses copy on write, so basically everything is a reference until you modify it, but for objects you need to use clone and the __clone() magic method like in the accepted answer.
Source: Stackoverflow.com