private classes inside namespaces

Question

Possible Duplicate:
Namespace only class visibility in C#/.NET ?

What I want is to have a class that is only accessible to other classes inside the same namespace without having to put the namespace in it's own assembly.

Is there a reason this is not possible in C#?

Edit: I have change the question a little, since the compiler tells me that private is not allowed. Can anyone tell me the reason for this?

Answer 1

This is not possible.

You can only restrict the access to the assembly containing the class using the internal modifier.

You could also restrict the access to the class to a single class by making the class a nested class. E.g. if you make class B a private nested class in class A, B will only be accessible by A.

I think these two options are the best you can do. If you really want to restrict the access to the namespace, you will have to put it in a separate assembly.

EDIT: To your second question: why a private class is not allowed. Private classes are only allowed if they are nested within another class. If you make a non-nested class private, what is its use? You cannot access it anyway, so you cannot do anything with it.

Answer 2

In addition to gehho's answer: namespace is just a part of the type name (which only allows for all types to have unique names) - that's why you cannot restrict access to types inside a namespace.

Answer 3

You can restrict the visibility to the current assembly by using an internal class.

However, you can allow another assembly to get visibility to your assembly using the InternalsVisibleTo attribute.

Example

Define MyInternalClass in assembly AssemblyOne :

[assembly: InternalsVisibleTo("AssemblyTwo")]

internal class MyClass {
    internal void DoSomeAction() { }
}

Then define another class in AssemblyTwo :

public class MyOtherClass
{
    public void DoAnotherAction()
    {
        MyClass c = new MyClass();
        c.DoSomeAction();
    }
}

Answer 4

Because you can add types to namespace in any other external assembly. Would types in same namespace, but different assembly see your "private types"?

If no, we have difficult behaviour to understand (one type from namespace could see your type, another - no). If yes, we have a contradiction with definition of "private", because types in different assemblies would have an access to "private" details of assembly.

Answer 5

You can declare arbitrary namespaces, so you could declare your own classes as part of the System namespace, for example. Of course, that will result in an error if Microsoft decides to add a class with the same name to their namespace.

Why do you want to have "namespace-visibility"? It would mean a special kind of public, since anyone could declare their class as being in the required namespace and thus access your classes.

If you want it as security feature, this will not work. If you want to declutter your namespace by hiding "internal" classes, you could have an Internals namespace underneath your main namespace, for example.