Issue with abstract classes

This is a discussion on Issue with abstract classes within the C# Programming forums, part of the General Programming Boards category; I am using a library of code which has some classes defined like such: Code: public abstract class A { ...

  1. #1
    l'Anziano DavidP's Avatar
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    Issue with abstract classes

    I am using a library of code which has some classes defined like such:

    Code:
    public abstract class A
    {
    ...stuff...
    }
    
    public class B : A
    {
    ...stuff...
    }
    So we have a class A and a class B which inherits from A. Class A is also abstract.

    Now, we then have some function somewhere in the code which declares an instance of class B, does some operations on that object, and then returns it to the caller. It, however, returns it as if it were an instance of class A. It is something like this:

    Code:
    public A ReturnInstanceOfA()
    {
    	B myobj = new B();
    	return B;
    }
    Now, as a client to this library, I would like to call this function which instantiates an object of class B and returns it to me, and I want to see it as being a B and not an A. So I do this:

    Code:
    B myobj = ReturnInstanceOfA() as B;
    Problem. I get this error: Cannot convert type 'A' to 'B' via a reference conversion, boxing conversion, unboxing conversion, wrapping conversion, or null type conversion


    How can I solve this issue?
    Last edited by DavidP; 08-18-2008 at 03:46 PM.
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  2. #2
    Confused Magos's Avatar
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    That compiles just fine for me, the problem lies elsewhere. Are you sure your code doesn't try to cast like this?
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