Php 简明教程
PHP - Cloning Objects
诸如“$obj1 = $obj2”的 PHP 语句只是创建对内存中同一对象的另一个引用。因此，属性的更改同时反映在原始对象和复制的对象中。PHP 中的 clone 关键字创建对象的浅拷贝。
A PHP statement such as "$obj1 = $obj2" merely creates another reference to the same object in memory. Hence, changes in attribute reflect both in original and duplicate object. The clone keyword in PHP creates a shallow copy of an object.
$obj2 = $obj1原始对象中的更改不会反映在浅拷贝中。
Changes in the original object do not reflect in the shallow copy.
Example
请看以下示例：
Take a look at the following example −
<?php
class foo {
var $var1 = 'Hello';
}
$x = new foo();
$y = $x; # reference copy
echo $x->var1 . " " . $y->var1 . PHP_EOL;
$x->var1 = "Hello World";
echo $x->var1 . " " . $y->var1 . PHP_EOL;
?>它将生成以下 output −
It will produce the following output −
Hello Hello
Hello World Hello World在第一种情况下， $y 只是 $x 的引用副本。因此， var1 属性的任何更改都会反映在两者中。
In the first case, $y is just a reference copy of $x. Hence, any change in var1 property reflects in both.
但是，如果我们将 $y 声明为 $x 的克隆，则原始对象中的任何更改都不会反映在其浅拷贝中。
However, if we declare $y as a clone of $x, then any change in the original object is not reflected in its shallow copy.
Example
请看以下示例：
Take a look at the following example −
<?php
class foo {
var $var1 = 'Hello World';
}
$x = new foo();
# shallow copy
$y = clone $x;
echo $x->var1 . " " . $y->var1 . PHP_EOL;
$x->var1 = "Hello PHP";
echo $x->var1 . " " . $y->var1 . PHP_EOL;
?>它将生成以下 output −
It will produce the following output −
Hello World Hello World
Hello PHP Hello WorldExample
在以下代码中， myclass 的属性之一是作为地址类对象的属性。myclass 的一个对象被赋值复制。其嵌入地址对象的任何值的变化会反映在两个对象中，但是名称属性的变化不会体现在克隆对象中。
In the following code, myclass has one of attributes as object of address class. An object of myclass is duplicated by assignment. Any change in the value of its embedded address object is reflected in both the objects, but change in the name property is not effected in the cloned object.
<?php
class address {
var $city="Nanded";
var $pin="431601";
function setaddr($arg1, $arg2) {
$this->city=$arg1;
$this->pin=$arg2;
}
}
class myclass {
var $name="Raja";
var $obj;
function setname($arg) {
$this->name=$arg;
}
}
$obj1=new myclass();
$obj1->obj=new address();
echo "original object\n";
print_r($obj1);
echo "\n";
$obj2=$obj1; # reference copy
$obj1->setname("Ravi");
$obj1->obj->setaddr("Mumbai", "400001");
echo "after change: Original object\n";
print_r($obj1);
echo "\nCopied object\n";
print_r($obj2);
?>它将生成以下 output −
It will produce the following output −
original object
myclass Object
(
[name] => Raja
[obj] => address Object
(
[city] => Nanded
[pin] => 431601
)
)
after change: Original object
myclass Object
(
[name] => Ravi
[obj] => address Object
(
[city] => Mumbai
[pin] => 400001
)
)
Copied object
myclass Object
(
[name] => Ravi
[obj] => address Object
(
[city] => Mumbai
[pin] => 400001
)
)Using the "clone" Keyword
在浅表副本中，任何是对其他变量引用的原始对象的属性都将保持引用。clone 关键字不会复制复制对象的包含对象。
In a shallow copy, any properties of the original object that are references to other variables will remain references. The clone keyword does not copy the contained objects of the copied objects.
我们现在创建 myclass 对象的克隆，以便 $obj2 是 $obj1 的克隆。我们将 $obj1 的 name 属性从 Raja 更改为 Ravi ，然后修改嵌入地址对象。属性更改不会反映在其克隆中，但是引用的地址对象将更改。
We now create a clone of myclass object, so that $obj2 is the clone of $obj1. We change the name property of $obj1 from Raja to Ravi, and also modify the embedded address object. The property change will not reflect in its clone, but the referred address object will be changed.
Example
请看以下示例：
Take a look at the following example −
<?php
class address {
var $city="Nanded";
var $pin="431601";
function setaddr($arg1, $arg2) {
$this->city=$arg1;
$this->pin=$arg2;
}
}
class myclass {
var $name="Raja";
var $obj;
function setname($arg) {
$this->name=$arg;
}
}
$obj1=new myclass();
$obj1->obj=new address();
echo "original object\n";
print_r($obj1);
echo "\n";
$obj2=clone $obj1; # clone copy
$obj1->setname("Ravi");
$obj1->obj->setaddr("Mumbai", "400001");
echo "after change: Original object\n";
print_r($obj1);
echo "\nCopied object\n";
print_r($obj2);
?>它将生成以下 output −
It will produce the following output −
original object
myclass Object
(
[name] => Raja
[obj] => address Object
(
[city] => Nanded
[pin] => 431601
)
)
after change: Original object
myclass Object
(
[name] => Ravi
[obj] => address Object
(
[city] => Mumbai
[pin] => 400001
)
)
Copied object
myclass Object
(
[name] => Raja
[obj] => address Object
(
[city] => Mumbai
[pin] => 400001
)
)Using __clone() Method
clone 关键字创建对象的浅表副本。克隆对象后，PHP 将对所有对象的属性执行浅表副本。是对其他变量引用的任何属性都将保持引用。因此，对原始对象执行的任何更改也将出现在克隆对象中。
The clone keyword creates a shallow copy of the object. When an object is cloned, PHP will perform a shallow copy of all of the object’s properties. Any properties that are references to other variables will remain references. Hence, any changes done to the original object will also appear in the cloned object.
如果您希望防止复制的对象自动更新，则需要使用 __clone() 方法创建对象的深表副本。它是 PHP 中的魔术方法之一。
If you wish to prevent the copied object to update automatically, we need to create a deep copy of the object with the __clone() method. It is one of the magic methods in PHP.
一旦克隆完成，如果定义了 _clone() 方法，系统就会调用新创建对象的 _clone() 方法，以允许需要更改的任何必要属性。
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
在上述示例中，我们有一个 myclass 对象，其中一个属性 $obj 保存对地址类的对象的引用。要实现深表副本，我们会覆盖 myclass 中的 __clone() 魔术方法。
In the above example, we have an object of myclass, one of its attributes $obj holding the reference to an object of address class. To achieve a deep copy, we override the __clone() magic method in myclass.
<?php
class address {
var $city="Nanded";
var $pin="431601";
function setaddr($arg1, $arg2) {
$this->city=$arg1;
$this->pin=$arg2;
}
}
class myclass {
var $name="Raja";
var $obj;
function setname($arg) {
$this->name=$arg;
}
public function __clone() {
$this->obj = clone $this->obj ;
}
}
$obj1=new myclass();
$obj1->obj=new address();
echo "original object\n";
print_r($obj1);
echo "\n";
$obj2=clone $obj1; # cloned deep copy
$obj1->setname("Ravi");
$obj1->obj->setaddr("Mumbai", "400001");
echo "after change: Original object\n";
print_r($obj1);
echo "\nCloned object\n";
print_r($obj2);
?>您现在会看到原始对象（我们更改地址属性）中的更改不会反映在克隆对象中，如下面的 output 所示。
You will now see that the changes in the original object (we change the address attributes) won’t reflect in the cloned object, as the following output shows −
original object
myclass Object
(
[name] => Raja
[obj] => address Object
(
[city] => Nanded
[pin] => 431601
)
)
after change: Original object
myclass Object
(
[name] => Ravi
[obj] => address Object
(
[city] => Mumbai
[pin] => 400001
)
)
Cloned object
myclass Object
(
[name] => Raja
[obj] => address Object
(
[city] => Nanded
[pin] => 431601
)
)