PHP Cloneable Object

Question

I went through this example on the PHP Manual.

<?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()
    {
        // Force a copy of this->object, otherwise
        // it will point to same object.
        $this->object1 = clone $this->object1;
        $this->object2 = clone $this->object2;
    }
}

$obj = new MyCloneable();

$obj->object1 = new SubObject();
$obj->object2 = new SubObject();

$obj2 = clone $obj;


print("Original Object:\n");
print_r($obj);

print("Cloned Object:\n");
print_r($obj2);

?>

When i execute this $obj2 = clone $obj; can someone explain me what happens actually ? Will this call MyCloneable Class's function __clone() or SubObject Class's public function __clone() ?

Step by step explanation would be more helpful. Thanks.

matewka · Accepted Answer · 2013-11-22 11:19:48Z

1

__clone function handles the clone keyword. Using

$obj2 = clone $obj;

could be represented as

$obj2 = $obj::__clone();

But that's obvious to you.

clone ... calls the __clone method of the MyCloneable class. It has nothing to do with the SubObject class. object1 and object2 are only properties of the $obj object which is of class MyCloneable.

Of course, when you call the clone, the object1 and object2 properties will be cloned but they'll still be the object's properties. The $obj2 will be of class MyCloneable.

Does my answer satisfy your needs?

EDIT:

clone keywords inside the MyCloneable::__clone() method are creating clones of the $object1 and $object2 properties. In practice, it gives nothing because you're assigning the clones to the makers of these clones.
What happens in MyCloneable::__clone() - it is calling SubObject::__clone() method which in fact does this:

$this->instance = ++self::$instances;

Notice that instances property is static so every time you create a new or clone an existing object, the instances increments.

edited Nov 22, 2013 at 11:19

answered Nov 22, 2013 at 11:03

matewka

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1 Comment

Catherine Tyler Over a year ago

Thanks for answering. When you said clone ... calls the __clone method of the MyCloneable class. There is another clone keyword in the __clone() of the MyCloneable class. What happens there actually?

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