Final-Schlüsselwort
In PHP4 the clone keyword isn't defined, if you want a compatible code (using a copy of an object) - use this fix:
$c = (PHP_VERSION < 5) ? $b : clone($b);
It is possible cause php checks function existence just before its calling.
Objekte klonen
Eine Kopie eines Objektes mit vollständig replizierten Eigenschaften zu erzeugen ist nicht immer das gewünschte Verhalten. Ein gutes Beispiel für die Notwendigkeit von Kopierkonstruktoren ist ein Objekt, welches ein GTK Fenster repräsentiert und dieses Objekt enthält die Ressource des GTK-Fensters. Wenn Sie ein Duplikat dieses Objektes erzeugen, könnten Sie ein neues Fenster mit gleichen Eigenschaften erzeugen wollen und das neue Objekt soll die Ressource des neuen Fensters speichern. Ein weiteres Beispiel ist ein Objekt, welches eine Referenz auf ein anderes Objekt, das es benutzt, hält und wenn das Vaterobjekt repliziert wird, will man eine neue Instanz dieses anderen Objektes erzeugen, damit das Replikat eine eigene Kopie besitzt.
Eine Objektkopie wird durch die Nutzung des clone Schlüsselwortes (welches wenn möglich die __clone()-Methode des Objektes aufruft) erzeugt. Die __clone()-Methode eines Objektes kann nicht direkt aufgerufen werden.
$kopie_des_objektes = clone $objekt;
Wenn ein Objekt geklont wird, wird PHP 5 eine seichte Kopie der Eigenschaften des Objektes durchführen. Alle Eigenschaften, die Referenzen auf andere Variablen sind, werden Referenzen bleiben.
Sobald der Klonvorgang abgeschlossen und eine __clone()- Methode definiert ist, so wird die __clone()-Methode des neu erzeugten Objekts aufgerufen, damit alle notwendigen Eigenschaften verändert werden können.
Beispiel #1 Ein Objekt klonen
<?php
class SubObject
{
static $instanzen = 0;
public $instanz;
public function __construct() {
$this->instanz = ++self::$instanzen;
}
public function __clone() {
$this->instanz = ++self::$instanzen;
}
}
class MyCloneable
{
public $objekt1;
public $objekt2;
function __clone()
{
// Erzwinge eine Kopie von this->object,
// andernfalls wird es auf das selbe Objekt zeigen
$this->objekt1 = clone $this->objekt1;
}
}
$obj = new MyCloneable();
$obj->objekt1 = new SubObject();
$obj->objekt2 = new SubObject();
$obj2 = clone $obj;
print("Original Objekt:\n");
print_r($obj);
print("geklontes Objekt:\n");
print_r($obj2);
?>
Das oben gezeigte Beispiel erzeugt folgende Ausgabe:
Original Objekt:
MyCloneable Object
(
[object1] => SubObject Object
(
[instanz] => 1
)
[object2] => SubObject Object
(
[instanz] => 2
)
)
geklontes Object:
MyCloneable Object
(
[objekt1] => SubObject Object
(
[instanz] => 3
)
[objekt2] => SubObject Object
(
[instanz] => 2
)
)
add a note
User Contributed NotesObjekte klonen
Mr.KTO
13-Jun-2007 10:00
13-Jun-2007 10:00
Alexey
08-Feb-2007 04:18
08-Feb-2007 04:18
To implement __clone() method in complex classes I use this simple function:
function clone_($some)
{
return (is_object($some)) ? clone $some : $some;
}
In this way I don't need to care about type of my class properties.
MakariVerslund at gmail dot com
22-Jan-2007 01:30
22-Jan-2007 01:30
I ran into the same problem of an array of objects inside of an object that I wanted to clone all pointing to the same objects. However, I agreed that serializing the data was not the answer. It was relatively simple, really:
public function __clone()
{
foreach ($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.
felix gilcher
22-Sep-2006 04:20
22-Sep-2006 04:20
Copying objects with
<?php
public function copy()
{
$serialized_contents = serialize($this);
return unserialize($serialized_contents);
}
?>
is a pretty dangerous thing. What if your objects hold references to very large shared objects? They all get copied as well. Serializing objects may break database connections and references. What you probably want to do is implement a proper __clone() method for each of your classes so that each object in your tree gets to decide what subobjects need to be copied and which ones should better remain untouched.
regards
felix
paul at accessdesigns dot org dot uk
03-Aug-2006 10:47
03-Aug-2006 10:47
I noticed when trying to clone a series of objects in a loop and and adding them to an array, the objects were still passed by reference, so all objects took the same value as the last object cloned and added to the array.
The solution was to use the copy function as below which truly clones objects.
Here is an example:
<?php
$temp = new $this->_doname;
foreach($rows as $id=>$row) {
$do = clone $temp;
$do->load($id);
$this->_dataobjects[]= clone $do;
}
?>
This results in every object having the same value.
However using:
<?php
$this->_dataobjects[]= $this->copy($do);
?>
with
<?php
public function copy()
{
$serialized_contents = serialize($this);
return unserialize($serialized_contents);
}
?>
Actually produces the expected result.
Paul Bain
olle dot remove_this dot suni at rdnsoftware dot com
16-May-2006 01:49
16-May-2006 01:49
As jorge dot villalobos at gmail dot com pointed out, the "__clone is NOT an override".
However, if one needs a true copy of an object (which has real copies of all subobjects too, not references), one can define a class method such as this to the object-to-be-cloned:
public function copy()
{
$serialized_contents = serialize($this);
return unserialize($serialized_contents);
}
The method makes a string representation of the object's contents (including subobjects), which can then be unserialized back to an object.
The method usage is simple:
$original_object = new MyCloneable(); //can have sub objects
$copied_object = $original_object->clone(); //only makes copies of the values, not references
With serialization, you surely don't have to worry about references, since serialized object is just simple text.
ove at junne dot dk
08-Feb-2006 05:02
08-Feb-2006 05:02
Consider this:
function myfunc()
{
$A = new myobject(); // Create another mysql connection
$A->method1(); // Runs a query (works)
}
$A = new myobject(); // Create a mysql connection
myfunc();
$A->method1(); // This query fails! Possible because leaving the function has closed the connection.
Conclusion: Declaration of objects within and outside a function WITH THE SAME NAME, will affect each other. Do not relay on the rules of scope.
Take care when using recursive structures!!
It took me a long time to figure out.
markus dot amsler at oribi dot org
20-Jun-2005 03:14
20-Jun-2005 03:14
For php4 you can use the clone method from the PEAR PHP_Compat package (http://pear.php.net/package/PHP_Compat).
jorge dot villalobos at gmail dot com
31-Mar-2005 01:29
31-Mar-2005 01:29
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.