How to create child object from existing parent object

Question

I have following php class

class User implements IUser
{
    public function __construct($i_objParent = NULL)
    {

    }
}

When I login successfully I create object of User class.

There is another class named Student class as follows which extends User Class

class Student extends User
{
    public function __construct($i_objParent = NULL)
    {
        parent::construct($i_objParent);
    }
}

Now as I said eariler I already have object of User class how can I construct Student object from existing User Class.

I think it may be possible by passing existing User class object to constructor of child class here Student class object?

Also, Is above approach OK?

Answer 1

As you cannot cast objects in php ( well there are really ugly hacks that work, but i would avoid them ).

Instead there are two ways:

• create a factory class which takes the User instance in returns you new Student instance with all the data transfered
• use Decorator pattern , which would call methods on User instance

Actually there is third way ( one that i would use ) : do not do this. PHP is not the language for DCI development paradigm. IMHO this whole construction makes no sense. User and Student are not interchangeable.