class X;

class Y
{
    friend void f(X const &);
};

void g(X const &);

int main()
{
    f(getX());
}

Every name first declared in a namespace is a member of that namespace. If a friend declaration in a non-local class first declares a class or function the friend class or function is a member of the innermost enclosing namespace. The name of the friend is not found by simple name lookup until a matching declaration is provided in that namespace scope (either before or after the class declaration granting friendship). If a friend function is called, its name may be found by the name lookup that considers functions from namespaces and classes associated with the types of the function arguments (3.4.2). When looking for a prior declaration of a class or a function declared as a friend, and when the name of the friend class or function is neither a qualified name nor a template-id, scopes outside the innermost enclosing namespace scope are not considered.

R>>char engine(...);

R>>template<typename, int> struct magic;
R>>typedef magic<char, -1> magicc;

R>>template<typename type = int, int id = sizeof(engine(*(magicc*)0, *(type*)0))>
R>>struct magic
R>>{
R>>    friend int engine(magicc&, type&);
R>>    static const int val = id;
R>>};

R>>int main()
R>>{
R>>    char a[magic<>::val != magic<>::val ? 1 : -1];
R>>}
R>>

E>А то я что-то никак не въеду

1
4
4
4

template <class T>
T& make();

template <int N>
struct Size
{
    typedef char (&type)[N];
};

///////////////////////////////////////////////////////////

Size<1>::type g(...);

template <int N>
class Z
{
    friend typename Size<N>::type g(Z<0> const &);
};

int main()
{
    std::cout << sizeof(g(make<Z<0> >())) << std::endl;
    new Z<2>;
    std::cout << sizeof(g(make<Z<0> >())) << std::endl;
}

R>Пришло время очередного ресёрча

namespace compile_time_flag
{
    struct yes{};
    struct no{char _no[2];};

    no check(...);
    template <class,class,int> struct flag;

    template <class T> T& make_ref();

    template <class flag_type,class type = yes, int id = sizeof(check(make_ref<flag<flag_type,no,-1> >(), make_ref<type>()))==sizeof(yes)>
    struct flag
    {
        friend yes check(flag<flag_type,no,-1>&,type&);
        static const int IsTrue = id;
    };
}

#include <iostream>

int main()
{
    char a[compile_time_flag::flag<int>::IsTrue != compile_time_flag::flag<int>::IsTrue ? 1 : -1];//Первый 0, второй 1
    static const int i = compile_time_flag::flag<char>::IsTrue;//0
    static const int j = compile_time_flag::flag<double>::IsTrue;//0
    static const int k = compile_time_flag::flag<double>::IsTrue;//1
    static const int l = compile_time_flag::flag<char>::IsTrue;//1
    static const int m = compile_time_flag::flag<char>::IsTrue;//1
    std::cout<<i<<j<<k<<l<<m;//00111
}

char a[compile_time_flag::flag<int>::IsTrue != compile_time_flag::flag<int>::IsTrue ? 1 : -1];

R>

namespace compile_time_flag
{
    struct yes{};
    struct no{char _no[2];};

    no check(...);
    template <class,class,int> struct flag;

    template <class T> T& make_ref();

    template <class flag_type,class type = yes, int id = sizeof(check(make_ref<flag<flag_type,no,-1> >(), make_ref<type>()))==sizeof(yes)>
    struct flag
    {
        friend yes check(flag<flag_type,no,-1>&,type&);
        static const int IsTrue = id;
    };
}

#include <iostream>

int main()
{
    char a[compile_time_flag::flag<int>::IsTrue ==0 ? 1 : -1];
    char b[compile_time_flag::flag<int>::IsTrue ==0 ? 1 : -1];
(void)a;
(void)b;

}

friend yes check(flag<flag_type,no,-1>&,type&);

T>Итак, объясните мне, почему Comeau работает так(желательно с указанием стандарта), или относим Comeau к не поддерживающим стандарт компиляторам и еще раз апплодируем идее

T>Всем заранее спасибо

char a[compile_time_flag::flag<int>::IsTrue != compile_time_flag::flag<int>::IsTrue ? 1 : -1];