[Bug libstdc++/59027] New: std::is_signed does not include check for is_arithmetic

[marc.mutz at kdab dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59027

            Bug ID: 59027
           Summary: std::is_signed does not include check for
                    is_arithmetic
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marc.mutz at kdab dot com

According to N3797 Table 49, both is_signed and is_unsigned should evaluate to
true_type only if the argument is_arithmetic, too. is_unsigned honours this,
but is_signed doesn't:

  template<typename _Tp,
           bool = is_arithmetic<_Tp>::value>
    struct __is_signed_helper
    : public false_type { };

  template<typename _Tp>
    struct __is_signed_helper<_Tp, true>
    : public integral_constant<bool, _Tp(-1) < _Tp(0)>
    { };

  /// is_signed
  template<typename _Tp>
    struct is_signed
    : public __is_signed_helper<_Tp>::type
    { };

  /// is_unsigned
  template<typename _Tp>
    struct is_unsigned
    : public __and_<is_arithmetic<_Tp>, __not_<is_signed<_Tp>>>::type
    { };