Are implicity/explicit conversion methods inherited in C#?

Question

I'm not sure what I'm doing wrong here. I have a generic class, which is basically a glorified integer, with a few methods for certain string formatting, as well as into/from string and int conversions:

public class Base
{
    protected int m_value;
    ...
    // From int
    public static implicit operator Base(int Value)
    {
        return new Base(Value);
    }
    ...
    // To string
    public static explicit operator string(Base Value)
    {
        return String.Format("${0:X6}", (int)Value);
    }
}

And it functions fine. I can successfully use implicit and explicit conversions:

Base b = 1;
Console.WriteLine((string)b);  // Outputs "$000001", as expected.

Then I derive from this class, different child classes, which turn on/off different named bits in m_value. For example:

public class Derived : Base
{

}

And then I cannot use my implicit to/from int conversions:

Derived d = 3;
// Cannot implicitly convert type 'int' to 'Derived'. An explicit conversion exists (are you missing a cast?)

Even this gives the same error:

Derived d = (int)3;

Are the implicit/explicit conversions not inherited in the derived class? This will require a lot of code copying if not.

RESPONSE Thank you so much for the quick responses! You all deserve the 'answer' checkmark, they're all very good answers. The key is to think about the types on both sides of the equal sign. Now that I think about it like that, it makes perfect sense.

I obviously only have to re-write my "to Derived" conversions. The "to Int32, String, etc" conversions still apply.

Answer 1

The reason

Derived d = (int)3;

does not work is because the type Derived does not exactly match the return value of the operator Base as is required to invoke this operator. Notice that you haven't provided any conversion operators that contain the code new Derived(...), so it is not surprising that you can't make new Derived instances this way.

Note, however, that the opposite conversion

Derived v = ...;
string s = (string)v;

will work fine (as if it were "inherited", although this is not really inheritance due to the static keyword).

Answer 2

No, it will not work that way. The compiler will not implicitly downcast from a base to a derived for you. Basically, you can't do ...

D d = new B();

You will get your base class implmentations from your string cast, because it will do the implicit upcasting for you.

You could do a work around if you didn't want to copy your methods to your derived class with an extension function on integers, like (assuming your derived class is called D) ...

public static class Ext
{
    public static D IntAsD(this int val)
    {
        return new D(val);
    }
}

Then, you could do what you want with ...

D d1 = 5.IntAsD();

Granted, it's not perfect, but it might fit your needs.