9 Declarations [dcl.dcl]

namespace X {
  void f() { /* ... */ }        // OK: introduces X​::​f()

  namespace M {
    void g();                   // OK: introduces X​::​M​::​g()
  }
  using M::g;
  void g();                     // error: conflicts with X​::​M​::​g()
}

namespace Q {
  namespace V {
    void f();
  }
  void V::f() { /* ... */ }     // OK
  void V::g() { /* ... */ }     // error: g() is not yet a member of V
  namespace V {
    void g();
  }
}

namespace R {
  void Q::V::g() { /* ... */ }  // error: R doesn't enclose Q
}

// Assume f and g have not yet been declared.
void h(int);
template <class T> void f2(T);
namespace A {
  class X {
    friend void f(X);           // A​::​f(X) is a friend
    class Y {
      friend void g();          // A​::​g is a friend
      friend void h(int);       // A​::​h is a friend
                                // ​::​h not considered
      friend void f2<>(int);    // ​::​f2<>(int) is a friend
    };
  };

  // A​::​f, A​::​g and A​::​h are not visible here
  X x;
  void g() { f(x); }            // definition of A​::​g
  void f(X) { /* ... */ }       // definition of A​::​f
  void h(int) { /* ... */ }     // definition of A​::​h
  // A​::​f, A​::​g and A​::​h are visible here and known to be friends
}

using A::x;

void h() {
  A::f(x);
  A::X::f(x);                   // error: f is not a member of A​::​X
  A::X::Y::g();                 // error: g is not a member of A​::​X​::​Y
}