Polymorphism in PHP (+ question on casting "up")

If I have the following class heirarchy:
>
class A{
protected $m_type;
>
function type(){return $this->m_type;}
}
>
class B extends A{}
class C extends B{}
>
class D{
private A $m_objref ; //reference to object of type A
>
//Is this possible?
public function foobar(A $obj){
switch($obj->type()){
case: 1 //treat as A
A $myvar_a = obj;
break;
>
case: 2 //treat as B (do I need an explicit cast here?)
B $myvar_b = obj;
break;
>
case: 3 //treat as C (do I need an explicit cast here?)
C $myvar_c = obj;
break;
}
}
}
}
>
>

Ronald Raygun wrote:
>>
Maybe a better question would be what are you actually trying to do?
>

>
>
Jerry Stuckle wrote:
>>
I have a session class that stores a user. There are different types of
users (with different methods), but they each derive from a base User
class. I want to have one single reference that points to the user object.
>
The case I make above helps to find out what the PHP language limits are
(not to mention "gotchas", if I make C++ like assumptions in my code).
>
On a more practical level, on pages where a user (of type B for example)
is expected, (after preliminary sanity checks), I will need to start
treating the variable as a variable of Type B, although it is stored as
a reference to a User (remember Class B is-a 'User'). This is where my
question about "casting down[corrected]" (the class diagram) comes in.
>
Can I simple sstart calling methods on the 'B' interface, or do I need
to make an explicit cast from 'User' to 'B', before using the object
retrieved from the session?
>

Can I simple sstart calling methods on the 'B' interface, or do I need
to make an explicit cast from 'User' to 'B', before using the object
retrieved from the session?

<snip>
>>
If you really want to check if the instance if of class/interface B, use
the instanceof operator. But if you already know it is of
class/interface B, you can just call the method.
>
If you are used to Visual Basic, this may be surprising to you. But an
interface in PHP just says "conforming objects are guaranteed to have
these methods". Interfaces in PHP do not hide or rename methods.