Why is it not possible to inherit a public class from an internal class? [duplicate]

Question

See this code:

internal class c 
{
    private int d;
}

public class a : c
{
    private int b;
}

Why can I not inherit a public class from an internal class? Why does the compiler have this behavior?

Answer 1

Because the public class would be visible outside your current assembly, while the internal one isn't. When deriving from a class you can only restrict visibility further, because in your case it would make the implementation of c available to consumers outside your assembly which kind of defeats the purpose of making the class internal in the first place.

You can use composition instead of inheritance, though.

Answer 2

C# design principle. Derived class should atleast have same accessibility as the parent class. In your case it is not hence not allowed. Take a look at Eric Lippert's view on this deriving public class from an internal class