type-safe constexpr comparison of ints

// http://stackoverflow.com/questions/16752954/
#include <type_traits>
#include <limits>
#include <utility>

#include <cstdint>
#include <cstdlib>

template< typename L, typename R >
inline constexpr
typename std::enable_if< (std::is_signed< L >::value && !std::is_signed< R >::value), bool >::type
less(L const & lhs, R const & rhs)
{
    static_assert(std::is_integral< L >::value,
                  "lhs value must be of integral type");
    static_assert(std::is_integral< R >::value,
                  "rhs value must be of integral type");
    using T = typename std::common_type< L, R >::type;
    return (lhs < static_cast< L >(0)) || (static_cast< T const & >(lhs) < static_cast< T const & >(rhs));
}

template< typename L, typename R >
inline constexpr
typename std::enable_if< (!std::is_signed< L >::value && std::is_signed< R >::value), bool >::type
less(L const & lhs, R const & rhs)
{
    static_assert(std::is_integral< L >::value,
                  "lhs value must be of integral type");
    static_assert(std::is_integral< R >::value,
                  "rhs value must be of integral type");
    using T = typename std::common_type< L, R >::type;
    return !(rhs < static_cast< R >(0)) && (static_cast< T const & >(lhs) < static_cast< T const & >(rhs));
}

template< typename L, typename R >
inline constexpr
typename std::enable_if< (std::is_signed< L >::value == std::is_signed< R >::value), bool >::type
less(L const & lhs, R const & rhs)
{
    static_assert(std::is_integral< L >::value,
                  "lhs value must be of integral type");
    static_assert(std::is_integral< R >::value,
                  "rhs value must be of integral type");
    return lhs < rhs;
}

namespace
{

static_assert(less(1, 2), "0");
static_assert(less(-1, std::numeric_limits< std::uintmax_t >::max()), "1");
static_assert(less< std::int8_t, std::uintmax_t >(-1, std::numeric_limits< std::uintmax_t >::max()), "2");
static_assert(less< std::intmax_t, std::uint8_t >(-1, std::numeric_limits< std::uint8_t >::max()), "3");
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wsign-compare"
static_assert(!(-1 < std::numeric_limits< unsigned long >::max()), "4");
#pragma GCC diagnostic pop
static_assert(less(-1, std::numeric_limits< unsigned long >::max()), "5");

}

int main()
{
        return EXIT_SUCCESS;
}