meta::totally_ordered

Defined in header <mgs/meta/concepts/totally_ordered.hpp>.

template <typename T>
concept totally_ordered =
  meta::equality_comparable<T> &&
  requires(std::remove_reference_t<T> const& a,
           std::remove_reference_t<T> const& b) {
  { a <  b } -> meta::boolean;
  { a >  b } -> meta::boolean;
  { a <= b } -> meta::boolean;
  { a >= b } -> meta::boolean;
};

Pre-C++20 implementation of the std::totally_ordered concept.

Concept emulation

namespace mgs {
namespace meta {

template <typename T>
struct is_totally_ordered { /* ... */ };

template <typename T>
constexpr auto is_totally_ordered_v =
                  is_totally_ordered<T>::value;

template <typename T,
          typename = std::enable_if_t<is_totally_ordered_v<T>>>
using totally_ordered = T;

} // namespace meta
} // namespace mgs

Example

#include <mgs/meta/concepts/totally_ordered.hpp>

using namespace mgs::meta;

struct ordered {};

bool operator==(ordered const&, ordered const&);
bool operator!=(ordered const&, ordered const&);
bool operator<(ordered const&, ordered const&);
bool operator>(ordered const&, ordered const&);
bool operator<=(ordered const&, ordered const&);
bool operator>=(ordered const&, ordered const&);

static_assert(is_totally_ordered_v<int>, "");
static_assert(is_totally_ordered_v<ordered>, "");