How to return subtype in overridden method of subclass in C#?

Question

I have a subclass with an over-ridden method that I know always returns a particular subtype of the return type declared in the base class. If I write the code this way, it

Answer 1

You can do this if you introduce an extra method to override (since you can't override and new a method with the same name in the same type):

abstract class BaseClass
{
    public BaseReturnType PolymorphicMethod()
    { return PolymorphicMethodCore();}

    protected abstract BaseReturnType PolymorphicMethodCore();
}

class DerivedClass : BaseClass
{
    protected override BaseReturnType PolymorphicMethodCore()
    { return PolymorphicMethod(); }

    public new DerivedReturnType PolymorphicMethod()
    { return new DerivedReturnType(); }
}

Now you have a PolymorphicMethod method at each level with the correct type.