10 union U {  union
11   U();
12   U(const U &);
13   U(U &&);
14   U &operator=(const U&);
15   U &operator=(U&&);
16   ~U();
23 U::U() {}  in U()  function in U
24 U::U(const U&) {}  in U()  function in U
25 U::U(U&&) {}  in U()  function in U
26 U &U::operator=(const U&) { return *this; }  in operator =()  argument
27 U &U::operator=(U &&) { return *this; }  in operator =()  argument
28 U::~U() {}  in ~U()