How to use php clone keyword

In PHP, the clone keyword can be used to clone objects. The syntax format is "clone object name = clone original object name;"; after the object is cloned successfully, their member methods, attributes and values ​​are exactly the same. of. If you want to reassign the member attributes of the cloned copy, you can use the "__clone()" method.

The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

PHP clone keyword (Clone object)

The object model in PHP calls objects by reference, but sometimes it is necessary to create a copy of the object. When changing the original object, you do not want to affect the object copy. . If you use the new keyword to re-create the object and then assign the same value to the properties, it will be cumbersome and error-prone. In PHP, you can clone an identical object based on an existing object. After cloning, the original object and the copy object are completely independent and do not interfere with each other.

In PHP, you can use the clone keyword to clone an object. The syntax format is as follows:

克隆对象名称 = clone 原对象名称;

Because the clone method actually copies the entire object's memory area and uses new object variables. Points to new memory, so the assigned object and the original object are independent of each other.

After the objects are successfully cloned, their member methods, properties, and values ​​are exactly the same. If you want to reassign the member attributes of the cloned copy, you can use the __clone() method.

【Example】The following uses a simple example to demonstrate the use of clone keyword.

<?php
    class Website{
        public $name, $url;
        public function __construct($name, $url){
            $this -> name = $name;
            $this -> url  = $url;
        }
        public function output(){
            echo $this -> name.&#39;，&#39;.$this -> url.&#39;<br>&#39;;
        }
    }
    $obj  = new Website(&#39;PHP中文网&#39;, &#39;https://www.php.cn/&#39;);
    $obj2 = clone $obj;
    $obj  -> output();
    $obj2 -> output();
    echo &#39;<pre class="brush:php;toolbar:false">&#39;;
    var_dump($obj);
    var_dump($obj2);
?>

The running results are as follows:

PHP中文网，https://www.php.cn/
PHP中文网，https://www.php.cn/
object(Website)#1 (2) {
  ["name"]=>
  string(16) "PHP中文网"
  ["url"]=>
  string(27) "https://www.php.cn/"
}
object(Website)#2 (2) {
  ["name"]=>
  string(16) "PHP中文网"
  ["url"]=>
  string(27) "https://www.php.cn/"
}

Note: If you use = to assign an object to a variable, then what you get will be a reference to the object, which can be changed through this variable The property's value will affect the original object.

__clone() magic method

#__clone() method cannot be called directly, only when an object is cloned through the clone keyword You can use this object to call the __clone() method. When creating a copy of an object, PHP checks whether the __clone() method exists. If it does not exist, then it calls the default __clone() method, copying all the properties of the object. If the __clone() method has been defined, then the __clone() method will be responsible for setting the properties of the new object. So in the __clone() method, you only need to override those properties that need to be changed.

__clone() method does not require any parameters. Here is an example to demonstrate:

<?php
    class Website{
        public $name, $url;
        public function __construct($name, $url){
            $this -> name = $name;
            $this -> url  = $url;
        }
        public function output(){
            echo $this -> name.&#39;，&#39;.$this -> url.&#39;<br>&#39;;
        }
        public function __clone(){
            $this -> name = &#39;PHP教程&#39;;
            $this -> url  = &#39;https://www.php.cn/&#39;;
        }
    }
    $obj  = new Website(&#39;PHP中文网&#39;, &#39;https://www.php.cn/&#39;);
    $obj2 = clone $obj;
    $obj  -> output();
    $obj2 -> output();
?>

The running results are as follows:

PHP中文网，https://www.php.cn/
PHP教程，https://www.php.cn/

Tips: If Setting an empty __clone() method with private access rights in the class can disable cloning.

Recommended learning: "PHP Video Tutorial"

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