Is someone able to tell whether the following piece of code (obtain by
distilling a much bigger and convoluted one) is valid C++?
When both statement A and statement B are present, g++ 2.6.0 says (on
line statement-A): "structure `A<int>::B' not yet defined". I cannot
understand why a friendship declaration should alter what's defined
and what's not (and why more so then the Z<B>& two lines below).

I haven't tested the code with other compilers because the only other
available to me doesn't come even near to understand nested
typed.

template<class T>
class Z {
    T::mode m;     // statement A
    int i;
};

template<class I>
Z<I>
f (const I& i)
{
    return Z<I>();
}

template<class T>
class A {
    class node {};
public:
    class B {
 friend Z<B> f (B&);   // statement B
    public:
 enum mode {normal, bfs, dfs};
 B& operator <<(const Z<B>& z) {return *this;}
    };
};


main() {
    A<int>::B b;

    b << f (b) ;
}

--
    Maurizio Vitale
 _______________
|        _      |\   e-mail: mav@cc.gatech.edu     | How many times can
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