Question

I have been thinking about a way solve a problem I have and I’m not sure whether it will work or not.

Say we have a base class called A and 3 subclass B,C and D.

        A
        ^
-----------------
|       |       |
B       C       D

Also we have three classes X, Y and Z.

On my system objects type B,C,D are passed as type A and usually I have to convert the Objects of type B,C,D to either objects X,Y or Z (That’s not a cast, I manually convert them since they are totally different).

Therefore, to convert an Object type A to a type X, Y or Z I need to check the subtype first and then initialize a X, Y or Z Object with the result of some operations about the A Object depending on the subtype.

I thought about overloading an explicit cast operation from A to X, Y or Z just doing the same process I was doing when I converted them, but then I thought… Would it be possible to use polimorfism and overload the cast from B,C and D in some way that when I add a new subtype of A I do not need to change the cast code of A?(Just add the explicit cast overload to the new subtype)

I hope I have explained myself properly sorry if there is something confusing.

NOTE: I will add a cast overload for X,Y,Z

Answer 1

You can have your cast operator for type A call a virtual (or abstract?) instance method of your A instance and override that for each subclass of A. X, Y and Z should derive from a mutual base class for this solution, though, so the cast operator can have that base class as a result type.

public abstract class A
{
    protected abstract W ConvertToW();

    public static explicit operator W(A a)
    {
        return a.ConvertToW();
    }
}

In this example, W is a base class of X, Y and Z.