Question

I have a function which accepts two base class parameters. Within this function I wish to test the types of these parameters over a number of derived classes and then call a polymorphic function. See below to see my first attempt which won’t compile.

    public static double Intersect(baseClass s0, baseClass s1)
    {
          if (s1 is derivedClassB) return (s0 as derivedClassA).PolyMethod((derivedClassB)s1);

          else if (s1 is derivedClassC) return (s0 as  derivedClassA).PolyMethod((derivedClassC)s1);
                    else return 0.0;

    }

I thought i could use something like

Type dType = s0.GetType();
(s0 as dType).PolyMethod(derivedClassB) s1);

but this doesn’t work either.

Answer 1

Define your base class like this

public abstract BaseClass
{
    public abstract double PolyMethod(BaseClass s);
}

Define derived classes like this

public DerviedClassX : BaseClass
{
    public override double PolyMethod(BaseClass s)
    {
        return 0.0; // Return something usefull here.
    }
}

Then your method can be simplified like this

public static double Intersect(BaseClass s0, BaseClass s1)
{
    return s0.PolyMethod(s1);
}