Question

How to check (without Boost or other nonstandard lib) if type passed to template is an enum type?
Thanks.

Answer 1

Looking at http://www.boost.org/doc/libs/1_44_0/boost/type_traits/is_enum.hpp,

If this evaluates to true:

::boost::type_traits::ice_or<
           ::boost::is_arithmetic<T>::value
         , ::boost::is_reference<T>::value
         , ::boost::is_function<T>::value
         , is_class_or_union<T>::value
         , is_array<T>::value
      >::value

Then this base template is selected:

// Don't evaluate convertibility to int_convertible unless the type
// is non-arithmetic. This suppresses warnings with GCC.
template <bool is_typename_arithmetic_or_reference = true>
struct is_enum_helper
{
    template <typename T> struct type
    {
        BOOST_STATIC_CONSTANT(bool, value = false);
    };
};

Otherwise check if it’s convertible to int:

template <>
struct is_enum_helper<false>
{
    template <typename T> struct type
       : ::boost::is_convertible<typename boost::add_reference<T>::type,::boost::detail::int_convertible>
    {
    };
};

If you want to do it as well as Boost, you’ll have to define all those other traits. <type_traits> is like that.