How make a class private inside a namespace in C++?

Question

How make a class private inside a namespace in C++ and prevent other to access the class from outside the namespace, for instance:

namespace company{
    class MyPublicClass{ ... }  // This should be accessible 
    class MyPrivateClass{ ... } // This should NOT be accessible
}

Answer 1

You can't have access specifiers for namespaces, but you can for classes:

class company {
    // Private (default)
    class MyPrivateClass { ... };

public:
    class MyPublicClass { ... };
};

You access the classes just like for a namespace with the scope operator:

company::MyPublicClass my_public_object;

If the "public" class should have access to the "private" class, then the "private" class have to be a friend of the `public" class.

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There is also another way, and that is to simply not have the MyPrivateClass definition in a public header file. Either define the class in the source file, or in a private header file only included internally.

Which way to choose depends on your design and use-cases.