[Bug c++/42013] cv-qualification of conditional expression type depending on the value of its first expression?!?

[paolo dot carlini at oracle dot com]

------- Comment #1 from paolo dot carlini at oracle dot com  2009-11-12 04:09 
-------
Actually, the observation about C++0x is largely incorrect, because the actual
specifications in DR 1255 are different, use std::add_rvalue_reference.

However, my main puzzlement stands.

Also, as regards the C++0x common_type (per DR 1255), I'm seeing the problem
with cv-qualified void, eg, replace in the snippet int -> void and const int ->
const void, because in that case std::add_rvalue_reference does nothing:

#include <type_traits>

template<typename _Tp>
  struct __declval_protector
  {
     static typename std::add_rvalue_reference<_Tp>::type __delegate();
  };

template<typename _Tp>
  typename std::add_rvalue_reference<_Tp>::type
  declval()
  {
    return __declval_protector<_Tp>::__delegate();
  }

template<typename _Tp, typename _Up>
  struct common_type
  {
    typedef __decltype(true  ? declval<_Tp>() : declval<_Up>()) typet;
    typedef __decltype(false ? declval<_Tp>() : declval<_Up>()) typef;
  };

template<typename, typename> struct is_same;

template<typename _Tp> struct is_same<_Tp, _Tp> { typedef _Tp type; };

void f()
{
  typedef common_type<void, const void>::typet typet;
  typedef common_type<void, const void>::typef typef;

  typedef is_same<typet, typef>::type type;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42013