What do you choose, protected or internal?

Question

If I have a class with a method I want protected and internal. I want that only derived classes in the assembly would be able to call it.

Since protected internal means protected or internal, you have to make a choice. What do you choose in this case - protected or internal?

Answer 1

I want that only derived classes in the assembly would be able to call it.

Well then, you have two choices. You can make it protected, and whenever one of your customers extends your class and calls your method and you find out about it, you can write them a sternly worded letter telling them to please stop doing that. Or you can make it internal, and do code reviews of your coworkers' code to ensure that they don't use the method they're not supposed to use.

My guess is that the latter is the cheaper and easier thing to do. I'd make it internal.

Answer 2

Personally I would choose protected. If subclasses in your own assembly are good enough to call the method, why wouldn't a subclass in another assembly? Perhaps you could refactor the functionality into a separate (internal) class altogether.

You really need to think objectively about the purpose of the method. Internal accessibility almost always feels wrong to me. Mostly because of my experience trying to derive from controls or classes in the .NET framework where I ran into a brick wall because someone decided to mark a class or method as internal. The original author never noticed that not having access to that method made things much harder to implement a subclass.

EDIT

To clarify, internal accessibility for a class is very useful and I wasn't implying internal in general is bad. My point was that internal methods on an otherwise public class seems wrong to me. A properly designed base class should not give an unfair advantage to derived classes in the same assembly.

Answer 3

I believe the right choice is internal. This way you can protect people outside of your assembly from calling this method, and this only leaves you to be careful and only call this method from derived classes. It is easier to be careful in the assembly you write than hope other people would be careful when they use it.

Answer 4

It's such a quirky decision to make protected internal mean protected OR internal. For this precise case I would use internal. The reason is that if encapsulation is broken, I would rather it'd be me, rather that someone not under my control.

Answer 5

I think the answer varies based on your needs. If I were you, I would do something like this:

    public class YourClass
    {
       protected class InnerClass
       {
           internal void YourMethod()
           {
               // Your Code
           }
       }
    }