Ключова дума final
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]
Клониране на обекти
Създаването на копие на обект с абсолютно идентични свойства не винаги е желаният вариант. Добър пример за необходимостта от копиране на конструкторите е ситуацията, в която имате обект, който представлява GTK прозорец и съдържа ресурсите на този GTK прозорец. Когато създадете копие на този обект, може да искате да създадете нов прозорец със същите свойства и новият обект да съдържа ресурсите на новия прозорец. Като друг пример може да послужи ситуацията, в която вашият обект използва референция към друг обект, който използва и когато създадете копие на родителския обект, искате да се създаде нова инстанция и на другия обект, така че и той да си има свое собствено копие.
Копие на обект се създава посредством ключовата дума clone (която извиква метода __clone() на обекта, ако е възможно). Методът __clone() не може да бъде извикан директно.
$copy_of_object = clone $object;
Когато се създаде копие на обекта, PHP5 ще създаде нова инстанция на обекта, с негово собствено копие на свойствата. Всички свойства, които са референции към други променливи ще си останат референции, т.е. няма да се извърши дълбочинно копиране. Ако е дефиниран метод __clone(), ще бъде извикан метода __clone() на новосъздадения обект, за да може в случай на нужда да се променят стойностите на някои свойства.
Example #1 Клониране на обект
<?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()
{
// Принуждава създаването на копие на $this->object, в противен случай
// ще сочи към същия обект.
$this->object1 = clone $this->object1;
}
}
$obj = new MyCloneable();
$obj->object1 = new SubObject();
$obj->object2 = new SubObject();
$obj2 = clone $obj;
print("Оригинален обект:\n");
print_r($obj);
print("Клониран обект:\n");
print_r($obj2);
?>
Примерът по-горе ще изведе:
Оригинален обект: MyCloneable Object ( [object1] => SubObject Object ( [instance] => 1 ) [object2] => SubObject Object ( [instance] => 2 ) ) Клониран обект: MyCloneable Object ( [object1] => SubObject Object ( [instance] => 3 ) [object2] => SubObject Object ( [instance] => 2 ) )
add a note
User Contributed NotesКлониране на обекти
wbcarts at juno dot com
02-Oct-2008 08:41
02-Oct-2008 08:41
Jim Brown
20-Jul-2008 12:34
20-Jul-2008 12:34
Regarding the generic deep __clone() example provided by david ashe at metabin:
If your object has a variable that stores an array of objects, that particular __clone() example will NOT perform a deep copy on your array of objects.
alex dot offshore at gmail dot com
19-May-2008 12:23
19-May-2008 12:23
Remember that in PHP 5 ALL objects are assigned BY REFERENCE.
<?php
function foo($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
crrodriguez at suse dot de
13-Mar-2008 06:52
13-Mar-2008 06:52
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.
Hayley Watson
18-Dec-2007 12:51
18-Dec-2007 12:51
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);
david ashe at metabin
02-Dec-2007 07:18
02-Dec-2007 07:18
Here is a function to clone all of the objects automatically
(useful if you use a base class that has this method)
function __clone(){
foreach($this as $name => $value){
if(gettype($value)=='object'){
$this->$name= clone($this->$name);
}
}
}
tomi at cumulo dot fi
13-Nov-2007 12:57
13-Nov-2007 12:57
It should be noticed that __clone() does not allow you to return a value. Basically the idea is that you implement this magic method only when you want to execute operations inside the cloned object, immediately prior to the cloning. In this way __clone() is similar to the default destructor (__destruct()), in that it executes code right before the object is destroyed.
muratyaman at gmail dot com
08-Oct-2007 04:43
08-Oct-2007 04:43
I think this is a bit awkward:
<?php
class A{
public $aaa;
}
class B{
public $a;
public $bbb;
function __clone(){
$this->a = clone $this->a;//clone MANUALLY!!!
}
}
$b1 = new B();
$b1->a = new A();
$b1->a->aaa = 111;
$b1->bbb = 1;
$b2 = clone $b1;
$b2->a->aaa = 222;//BEWARE!!
$b2->bbb = 2;//no problem on basic types
var_dump($b1); echo '<br />';
var_dump($b2);
/*
OUTPUT BEFORE implementing the function __clone()
object(B)#2 (3) { ["a"]=> object(A)#3 (1) { ["aaa"]=> int(222) } ["bbb"]=> int(1) }
object(B)#4 (3) { ["a"]=> object(A)#3 (1) { ["aaa"]=> int(222) } ["bbb"]=> int(2) }
OUTPUT AFTER implementing the function __clone()
object(B)#1 (3) { ["a"]=> object(A)#2 (1) { ["aaa"]=> int(111) } ["bbb"]=> int(1) }
object(B)#3 (3) { ["a"]=> object(A)#4 (1) { ["aaa"]=> int(222) } ["bbb"]=> int(2) }
*/
?>
Whenever we use another class inside, we must clone it manually. If you have 10s of classes related, this is rather tedious. I don't want to even think about classes dynamically populated with other objects. Be careful when designing your classes! You should look after your objects all the time! This major change on PHP5 vs PHP4 regarding "references" definitely has very good performance improvements but comes with very dangerous side effects as well..
Alexey
08-Feb-2007 04:18
08-Feb-2007 04:18
To implement __clone() method in complex classes I use this simple function:
function clone_($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.
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.