none.h

#pragma once
 
#include <ozo/core/concept.h>
#include <type_traits>
 
namespace ozo {
 
struct none_t {
    using type = void;
    template <typename ...Args>
    constexpr void operator() (Args&& ...) const noexcept {}
    template <typename ...Args>
    static constexpr void apply (Args&& ...) noexcept {}
};
 
constexpr auto none = none_t{};
 
template <>
struct is_time_constraint<none_t> : std::true_type {};
 
inline constexpr std::true_type operator == (const none_t&, const none_t&) { return {};}
 
template <typename T>
inline constexpr std::false_type operator == (const none_t&, const T&) { return {};}
 
template <typename T>
inline constexpr std::false_type operator == (const T&, const none_t&) { return {};}
 
inline constexpr std::false_type operator != (const none_t&, const none_t&) { return {};}
 
template <typename T>
inline constexpr std::true_type operator != (const none_t&, const T&) { return {};}
 
template <typename T>
inline constexpr std::true_type operator != (const T&, const none_t&) { return {};}
 
template <typename T>
using is_none = decltype(std::declval<const T&>() == none);
 
template <typename T>
inline constexpr auto IsNone = is_none<std::decay_t<T>>::value;
 
} // namespace ozo