What Does Protected Internal Mean?

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Pop quiz for you C# developers out there. Will the following code compile?

//In Foo.dll
public class Kitty
  protected internal virtual void MakeSomeNoise()
    Console.WriteLine("I'm in ur serverz fixing things...");

//In Bar.dll
public class Lion : Kitty
  protected override void MakeSomeNoise()

If you had asked me that yesterday, I would have said hell no. You can’t override an internal method in another assembly.

Of course, I would have been WRONG!

Well the truth of the matter is, I was wrong. This came up in an internal discussion in which I was unfairly complaining that certain methods I needed to override were internal. In fact, they were protected internal. Doesn’t that mean that the method is both protected and internal?

Had I simply tried to override them, I would have learned that my assumption was wrong. For the record...

protected internal means protected OR internal

It’s very clear when you think of the keywords as the union of accessibility rather than the intersection. Thus protected internal means the method is accessible by anything that can access the protected method UNION with anything that can access the internal method.

A Donkey Named Lester - Creative Commons By Attribution -
ninjapoodlesAs the old saying goes, when you assume, you make an ass out of u and me. I never understood this saying because when I assume, I only make an ass of me. I really think the word should simply be assme. As in... 

Never assme something won’t work without at least trying it.

UPDATE: Eilon, sent me an email to point out that...

BTW the CLR does have the notion of ProtectedANDInternal, but C# has no syntax to specify it. If you look at the CLR’s System.Reflection.MethodAttributes enum you’ll see both FamANDAssem as well as FamORAssem (“Family” is the CLR’s term for C#’s protected and “Assem” is C#’s internal).

If you don’t know Eilon, he’s a freaking sharp developer I get to work with on the MVC project and was the one who kindly disabused me of my ignorance on this subject. He keeps a blog at http://weblogs.asp.net/leftslipper/.

Apparently he’s the one with the clever idea of using a C# 3.0 anonymous type as a dictionary, that many of you saw in ScottGu’s ALT.NET Conference talk. Very cool.