Clônage d'objets

Le fait de créer une copie d'un objet possédant exactement les mêmes propriétés n'est pas toujours le comportement que l'on souhaite. Un bon exemple pour illustrer le besoin d'un constructeur de copie : si vous avez un objet qui représente une fenêtre GTK et que l'objet contient la ressource représentant cette fenêtre GTK, lorsque vous créez une copie vous pouvez vouloir créer une nouvelle fenêtre avec les mêmes propriétés, mais que le nouvel objet contienne une ressource représentant la nouvelle fenêtre.

Une copie d'objet est créée en utilisant le mot-clé clone (qui fait appel à la méthode __clone() de l'objet, si elle a été définie). La méthode __clone() d'un objet ne peut être appelée directement.

<?php

$copie_d_objet = clone $objet;

?>

Lorsqu'un objet est cloné, PHP effectue une copie superficielle de toutes les propriétés de l'objet. Toutes les propriétés qui sont des références à d'autres variables demeureront des références.

void __clone ( void )

Une fois le clonage effectué, si une méthode __clone() est définie, la méthode __clone() du nouvel objet sera appelée, pour permettre à chaque propriété qui doit l'être d'être modifiée.

Exemple #1 Exemple de duplication d'objets

<?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 
$objet1;
  public 
$objet2;

  function 
__clone() 
  {    
    
// Force la copie de this->object, sinon
    // il pointera vers le même objet.
    
$this->object1 = clone $this->object1;
  }
}

$obj = new MyCloneable();

$obj->object1 = new SubObject();
$obj->object2 = new SubObject();

$obj2 = clone $obj;


print(
"Objet original :\n");
print_r($obj);

print(
"Objet cloné :\n");
print_r($obj2);

?>

L'exemple ci-dessus va afficher :

Object original :
MyCloneable Object
(
    [object1] => SubObject Object
        (
            [instance] => 1
        )

    [object2] => SubObject Object
        (
            [instance] => 2
        )

)
Object cloné :
MyCloneable Object
(
    [object1] => SubObject Object
        (
            [instance] => 3
        )

    [object2] => SubObject Object
        (
            [instance] => 2
        )

)
add a note add a note

User Contributed Notes 20 notes

up
12
MakariVerslund at gmail dot com
7 years ago
I ran into the same problem of an array of objects inside of an object that I wanted to clone all pointing to the same objects. However, I agreed that serializing the data was not the answer. It was relatively simple, really:

public function __clone() {
    foreach ($this->varName as &$a) {
        foreach ($a as &$b) {
            $b = clone $b;
        }
    }
}

Note, that I was working with a multi-dimensional array and I was not using the Key=>Value pair system, but basically, the point is that if you use foreach, you need to specify that the copied data is to be accessed by reference.
up
4
Hayley Watson
7 years ago
It should go without saying that if you have circular references, where a property of object A refers to object B while a property of B refers to A (or more indirect loops than that), then you'll be glad that clone does NOT automatically make a deep copy!

<?php

class Foo
{
    var
$that;

function
__clone()
{
   
$this->that = clone $this->that;
}

}

$a = new Foo;
$b = new Foo;
$a->that = $b;
$b->that = $a;

$c = clone $a;
echo
'What happened?';
var_dump($c);
up
10
jojor at gmx dot net
4 years ago
Here is test script i wrote to test the behaviour of clone when i have arrays with primitive values in my class - as an additonal test of the note below by jeffrey at whinger dot nl

<pre>
<?php

class MyClass {

    private
$myArray = array();
    function
pushSomethingToArray($var) {
       
array_push($this->myArray, $var);
    }
    function
getArray() {
        return
$this->myArray;
    }

}

//push some values to the myArray of Mainclass
$myObj = new MyClass();
$myObj->pushSomethingToArray('blue');
$myObj->pushSomethingToArray('orange');
$myObjClone = clone $myObj;
$myObj->pushSomethingToArray('pink');

//testing
print_r($myObj->getArray());     //Array([0] => blue,[1] => orange,[2] => pink)
print_r($myObjClone->getArray());//Array([0] => blue,[1] => orange)
//so array  cloned

?>
</pre>
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3
crrodriguez at suse dot de
6 years ago
Keep in mind that since PHP 5.2.5, trying to clone a non-object correctly results in a fatal error, this differs from previous versions where only a Warning was thrown.
up
1
jorge dot villalobos at gmail dot com
9 years ago
I think it's relevant to note that __clone is NOT an override. As the example shows, the normal cloning process always occurs, and it's the responsibility of the __clone method to "mend" any "wrong" action performed by it.
up
3
ben at last dot fm
5 years ago
Here are some cloning and reference gotchas we came up against at Last.fm.

1. PHP treats variables as either 'values types' or 'reference types', where the difference is supposed to be transparent. Object cloning is one of the few times when it can make a big difference. I know of no programmatic way to tell if a variable is intrinsically a value or reference type. There IS however a non-programmatic ways to tell if an object property is value or reference type:

<?php

class A { var $p; }

$a = new A;
$a->p = 'Hello'; // $a->p is a value type
var_dump($a);

/*
object(A)#1 (1) {
  ["p"]=>
  string(5) "Hello" // <-- no &
}
*/

$ref =& $a->p; // note that this CONVERTS $a->p into a reference type!!
var_dump($a);

/*
object(A)#1 (1) {
  ["p"]=>
  &string(5) "Hello" // <-- note the &, this indicates it's a reference.
}
*/

?>

2. unsetting all-but-one of the references will convert the remaining reference back into a value. Continuing from the previous example:

<?php

unset($ref);
var_dump($a);

/*
object(A)#1 (1) {
  ["p"]=>
  string(5) "Hello"
}
*/

?>

I interpret this as the reference-count jumping from 2 straight to 0. However...

2. It IS possible to create a reference with a reference count of 1 - i.e. to convert an property from value type to reference type, without any extra references. All you have to do is declare that it refers to itself. This is HIGHLY idiosyncratic, but nevertheless it works. This leads to the observation that although the manual states that 'Any properties that are references to other variables, will remain references,' this is not strictly true. Any variables that are references, even to *themselves* (not necessarily to other variables), will be copied by reference rather than by value.

Here's an example to demonstrate:

<?php

class ByVal
{
    var
$prop;
}

class
ByRef
{
    var
$prop;
    function
__construct() { $this->prop =& $this->prop; }
}

$a = new ByVal;
$a->prop = 1;
$b = clone $a;
$b->prop = 2; // $a->prop remains at 1

$a = new ByRef;
$a->prop = 1;
$b = clone $a;
$b->prop = 2; // $a->prop is now 2

?>
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3
walkman at walkman dot pk
3 years ago
If you want a property that gets the same value in every clone if changed, you can do this simple trick:

<?php

class A
{
    public
$name ;
   
    public function
__construct()
    {
       
$this->name = & $this->name;
    }
}

$a = new A;
$a->name = "George";

$b = clone $a;
$b->name = "Somebody else";

var_dump($a);
var_dump($b);
?>

this will output:

object(A)#1 (1) {
  ["name"]=>
  &string(13) "Somebody else"
}
object(A)#2 (1) {
  ["name"]=>
  &string(13) "Somebody else"
}

You can change any of the clones property and all of the others will change accordingly.
up
2
Alexey
7 years ago
To implement __clone() method in complex classes I use this simple function:

function clone_($some)
{
   return (is_object($some)) ? clone $some : $some;
}

In this way I don't need to care about type of my class properties.
up
0
stanislav dot eckert at vizson dot de
5 days ago
This base class automatically clones attributes of type object or array values of type object recursively. Just inherit your own classes from this base class.

<?php
   
class clone_base
   
{
        public function
__clone()
        {
           
$object_vars = get_object_vars($this);

            foreach (
$object_vars as $attr_name => $attr_value)
            {
                if (
is_object($this->$attr_name))
                {
                   
$this->$attr_name = clone $this->$attr_name;
                }
                else if (
is_array($this->$attr_name))
                {
                   
// Note: This copies only one dimension arrays
                   
foreach ($this->$attr_name as &$attr_array_value)
                    {
                        if (
is_object($attr_array_value))
                        {
                           
$attr_array_value = clone $attr_array_value;
                        }
                        unset(
$attr_array_value);
                    }
                }
            }
        }
    }
?>

Example:
<?php
   
class foo extends clone_base
   
{
        public
$attr = "Hello";
        public
$b = null;
        public
$attr2 = array();

        public function
__construct()
        {
           
$this->b = new bar("World");
           
$this->attr2[] = new bar("What's");
           
$this->attr2[] = new bar("up?");
        }
    }

    class
bar extends clone_base
   
{
        public
$attr;

        public function
__construct($attr_value)
        {
           
$this->attr = $attr_value;
        }
    }

    echo
"<pre>";

   
$f1 = new foo();
   
$f2 = clone $f1;
   
$f2->attr = "James";
   
$f2->b->attr = "Bond";
   
$f2->attr2[0]->attr = "Agent";
   
$f2->attr2[1]->attr = "007";

    echo
"f1.attr = " . $f1->attr . "\n";
    echo
"f1.b.attr = " . $f1->b->attr . "\n";
    echo
"f1.attr2[0] = " . $f1->attr2[0]->attr . "\n";
    echo
"f1.attr2[1] = " . $f1->attr2[1]->attr . "\n";
    echo
"\n";
    echo
"f2.attr = " . $f2->attr . "\n";
    echo
"f2.b.attr = " . $f2->b->attr . "\n";
    echo
"f2.attr2[0] = " . $f2->attr2[0]->attr . "\n";
    echo
"f2.attr2[1] = " . $f2->attr2[1]->attr . "\n";
?>
up
0
olivier dot pons at goo dot without dot oo dot mail dot com
4 years ago
If you think "clone" will create a new instance, thus calling "__constructor", you're wrong. clone seems to only allocate memory for the object cloned, and simply copies the variables memory from the original to the new one (imagine something alike memcpy() in C). Nothing more. Keep in mind you'll have to do all the rest by yourself.
up
0
emile at webflow dot nl
4 years ago
Another gotcha I encountered: like __construct and __desctruct, you must call parent::__clone() yourself from inside a child's __clone() function. The manual kind of got me on the wrong foot here: "An object's __clone() method cannot be called directly."
up
0
koyama
5 years ago
The __clone() method for deep cloning by cheetah at tanabi dot org also works when the object to be cloned contains references to itself. This is not the case for any variation of the __clone() method in edit by danbrown at php dot net.

We are taking advantage of the fact that one can serialize an object that references itself.

Example:

<?php
class Foo
{
    function
__construct()
    {
       
$this->_myself = $this;
    }

    function
__clone() {
        foreach (
$this as $key => $val) {
            if (
is_object($val) || (is_array($val))) {
               
$this->{$key} = unserialize(serialize($val));
            }
        }
    }
}

// this object references itself
$foo = new Foo();

// create a deep clone
$bar = clone $foo;

// check if we reach this point
echo 'Finished cloning!';
?>

Replacing the __clone() method with the one shown in edit by danbrown at php dot net we run into an infinite loop, and we never get message 'Finished cloning!'.
up
0
wbcarts at juno dot com
6 years ago
CLONED ARMIES? USE STATIC DATA

When I think of cloning, I always think of Star Wars "Cloned Army"... where the number of clones are in the hundreds of thousands. So far, I have only seen examples of one or two clones with either shallow, deep, or recursive references. My fix is to use the static keyword. With static, you choose the properties your objects share... and makes scaling up the number of so-called "clones" much easier.

<?php

class Soldier {
  public static
$status;           // this is the property I'm trying to clone

 
protected static $idCount = 0;   // used to increment ID numbers
 
protected $id;                   // each Soldier will have a unique ID

 
public function __construct() {
   
$this->id = ++self::$idCount;
  } 

  public function
issueCommand($task) {
    switch(
$task){
      case
'Deploy Troops': self::$status = 'deploying'; break;
      case
'March Forward': self::$status = 'marching forward'; break;
      case
'Fire!': self::$status = 'shot fired'; break;
      case
'Retreat!': self::$status = 'course reversed'; break;
      default:
self::$status = 'at ease'; break;
    }
    echo
'COMMAND ISSUED: ' . $task . '<br>';
  }

  public function
__toString() {
    return
"Soldier[id=$this->id, status=" . self::$status . ']';
  }
}

# create the General and the Cloned Army
$general = new Soldier();
$platoon = array();
  for(
$i = 0; $i < 250; $i++) $platoon[] = new Soldier();

# issue commands, then check what soldiers are doing
$general->issueCommand('Deploy Troops');
echo
$general . '<br>';
echo
$platoon[223] . '<br>';
echo
$platoon[12] . '<br>';

$general->issueCommand('March Forward');
echo
$platoon[47] . '<br>';
echo
$platoon[163] . '<br>';

$general->issueCommand('Fire!');
echo
$platoon[248] . '<br>';
echo
$platoon[68] . '<br>';

$general->issueCommand('Retreat!');
echo
$platoon[26] . '<br>';
echo
$platoon[197] . '<br>';
?>

COMMAND ISSUED: Deploy Troops
  Soldier[id=1, status=deploying]
  Soldier[id=225, status=deploying]
  Soldier[id=14, status=deploying]

COMMAND ISSUED: March Forward
  Soldier[id=49, status=marching forward]
  Soldier[id=165, status=marching forward]

COMMAND ISSUED: Fire!
  Soldier[id=250, status=shot fired]
  Soldier[id=70, status=shot fired]

COMMAND ISSUED: Retreat!
  Soldier[id=28, status=course reversed]
  Soldier[id=199, status=course reversed]
up
0
Jim Brown
6 years ago
Regarding the generic deep __clone() example provided by david ashe at metabin:

If your object has a variable that stores an array of objects, that particular __clone() example will NOT perform a deep copy on your array of objects.
up
0
alex dot offshore at gmail dot com
6 years ago
Remember that in PHP 5 ALL objects are assigned BY REFERENCE.

<?php

 
function foo($a) // notice that '&' near $a is missing
 
{
   
$a['bar'] = 10;
  }

 
$x = array('bar' => 0); // built-in array() is not an object
 
$y = new ArrayObject(array('bar' => 0));

  echo
"\$x['bar'] == ${x['bar']};\n\$y['bar'] == ${y['bar']};\n\n";

 
foo($x);
 
foo($y);

  echo
"\$x['bar'] == ${x['bar']};\n\$y['bar'] == ${y['bar']};\n";

?>

Output:
$x['bar'] == 0;
$y['bar'] == 0;

$x['bar'] == 0;
$y['bar'] == 10;

Hope this will be useful.

By the way, to determine whether the variable is compatible with ArrayAccess/ArrayObject see http://php.net/manual/en/function.is-array.php#48083
up
-1
obaidmaroof at gmail dot com
7 months ago
<?php
class A{
  public
$my_var;
  function
__construct() { $this->my_var = 'aaa'; }
  }
 
 
$a = new A;
 
$b = clone $a;
 
$b->my_var = 'bbb';
 
  echo(
$a->my_var);   // 'aaa'
 
echo($b->my_var);   // 'bbb'

 
$c = new A;
 
$d = $c;
 
$d->my_var = 'bbb';
 
  echo(
$c->my_var);   // 'bbb'
 
echo($d->my_var);   // 'bbb'
?>

simple example to understand the basic concept behind clone.
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-1
cheetah at tanabi dot org
6 years ago
Want deep cloning without too much hassle?

<?php
function __clone() {
    foreach(
$this as $key => $val) {
        if(
is_object($val)||(is_array($val))){
           
$this->{$key} = unserialize(serialize($val));
        }
    }
}
?>

That will insure any object, or array that may potentially contain objects, will get cloned without using recursion or other support methods.



[EDIT BY danbrown AT php DOT net: An almost exact function was contributed on 02-DEC-2008-10:18 by (david ashe AT metabin):

<?php
   
function __clone(){
        foreach(
$this as $name => $value){
            if(
gettype($value)=='object'){
               
$this->$name= clone($this->$name);
            }
        }
    }
?>

Giving credit where it's due.  ~DPB]
up
-1
henke at henke37 dot cjb dot net
4 years ago
Arrays are shallow cloned on assignment, so don't use the clone keyword on them, just assign it to a new variable. That would lead to an error instead.
up
-2
seriously at something dot com
2 years ago
If you want a property that gets the same value in every clone if changed, you can do this simple trick:

<?php

class A
{
    public static
$name ;

}

$a = new A;
$a::$name = 'George';

$b = clone $a;
$b::$name = "Somebody else";

echo
'a: ' . $a::$name . "\n";
echo
'b: ' . $b::$name . "\n";

?>

this will output:

a: Somebody else
b: Somebody else

You can change any of the clones property and all of the others will change accordingly.
up
-3
jeffrey at whinger dot nl
4 years ago
For me it wasn't very clear to how this cloning of objects really worked so I made this little bit of code:

<?php
class foo
{
    public
$test;
   
    public function
test()
    {
        echo
'give us a '.$this->test."<br>\n";
    }
}

class
bar
{
    public
$foo;
   
    public function
insertFoo($foo)
    {
       
$this->foo = $foo;
    }
}

$foo = new foo();

$foo->test = 'foo';

$bar = new bar();

$bar->insertFoo($foo);

$foo->test();

$bar->foo->test();

$foo->test = 'bar';

$foo->test();

$bar->foo->test();

$bar->foo = clone $foo;

$bar->foo->test = 'woop woop';

$foo->test();

$bar->foo->test();

// result:
// give us a foo
// give us a foo
// give us a bar
// give us a bar
// give us a bar
// give us a woop woop
?>
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