Scope Resolution in C++

namespace X {
  class Y {
    static int i;
  public:
    void f();
  };
  class Z;
  void func();
}
int X::Y::i = 9;
class X::Z {
  int u, v, w;
public:
  Z(int i);
  int g();
};
X::Z::Z(int i) { u = v = w = i; }
int X::Z::g() { return u = v = w = 0; }
void X::func() {
  X::Z a(1);
  a.g();
}
int main(){} ///:~