[php classes and objects] object copy

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Object replication

Usage scenarios:

1. If you have a GTK window object, the object holds window-related resources. You may want to copy a new window, keeping all the same properties as the original window, but it must be a new object (because if it is not a new object, changes in one window will affect the other window).

2. If object A stores a reference to object B, when you copy object A, and you want the object used in it to be no longer object B but a copy of B, then you must get object A a copy of .

Implementation: Through the clone keyword (this will call the object's __clone() method if possible), the __clone() method in the object cannot be called directly.

    $copy_of_object = clone $object;

When an object is copied, PHP 5 will perform a shallow copy of all properties of the object. All reference properties will still be references to the original variables.

    void __clone ( void )

When copying is completed, if the __clone() method is defined, the __clone() method in the newly created object (the object generated by copying) will be called and can be used to modify the value of the attribute ( if necessary).

Example #1 复制一个对象<?phpclass 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()
    {

        // 强制复制一份this->object， 否则仍然指向同一个对象
        $this->object1 = clone $this->object1;
    }
}$obj = new MyCloneable();$obj->object1 = new SubObject();$obj->object2 = new SubObject();$obj2 = clone $obj;print("Original Object:\n");
print_r($obj);/*
Original Object:
MyCloneable Object
(
    [object1] => SubObject Object
        (
            [instance] => 1
        )

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

)
*/print("Cloned Object:\n");
print_r($obj2);/*
Cloned Object:
MyCloneable Object
(
    [object1] => SubObject Object
        (
            [instance] => 3
        )

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

)
*/?>

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