TITLE: Friends and nested classes and enums


PROBLEM: doug@foxtrot.ccmrc.ucsb.edu (Douglas Scott)

Given the following class:

class Outer {
private:
	enum PrivateEnum { Foo, Bar };
	friend class Inner;
	class Inner {
	public:
		Inner(int i= Foo) : myInt(i) {} // error here
		Inner() : myInt(Foo) {}     	// this also is an error
	private:
		int myInt;
	};
};

Why is it that Outer::Foo is not accessible to the constructor of
Outer::Inner, given that it is forward-declared as a friend class?


RESPONSE: clamage@Eng.Sun.COM (Steve Clamage), 7 Feb 95

The problem is that the friend declaration does not declare Outer::Inner
to be a friend, because that name isn't visible yet. It declares a
hypothetical file-scope Inner to be a friend. To make Outer::Inner
a friend, you either have to move the friend declaration after the
Inner class definition, or add a forward nested declaration for Inner.
The language rules were previously vague on this point, but a recent
clarification of those rules by the C++ Committee allows this:

class Outer {
	class Inner; // forward declare Outer::Inner
	friend class Inner; // make it a friend
	class Inner { ... };
};

It may be that your compiler doesn't follow the rule clarification yet, in
which case you have yet another workaround:

class Outer {
    enum PrivateEnum { Foo, Bar };
    class Inner {
	Inner(int); // can't specify a default parameter yet
	int x;
    };
    friend class Inner;
public:
    Outer();
};
Outer::Inner::Inner(int i = Foo) : ... // now we can specify the default
{ ... }