include/nlohmann/detail/meta/detected.hpp - develop - githubmirror/json

include/nlohmann/detail/meta/detected.hpp
70 строк2 KB
Niels Lohmann
:page_facing_up: adjust year (#5044)
01 янв 2026, 22:00
01 янв 2026, 22:00515d994
//     __ _____ _____ _____
//  __|  |   __|     |   | |  JSON for Modern C++
// |  |  |__   |  |  | | | |  version 3.12.0
// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
//
// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
// SPDX-License-Identifier: MIT

#pragma once

#include <type_traits>

#include <nlohmann/detail/meta/void_t.hpp>

NLOHMANN_JSON_NAMESPACE_BEGIN
namespace detail
{

// https://en.cppreference.com/w/cpp/experimental/is_detected
struct nonesuch
{
    nonesuch() = delete;
    ~nonesuch() = delete;
    nonesuch(nonesuch const&) = delete;
    nonesuch(nonesuch const&&) = delete;
    void operator=(nonesuch const&) = delete;
    void operator=(nonesuch&&) = delete;
};

template<class Default,
         class AlwaysVoid,
         template<class...> class Op,
         class... Args>
struct detector
{
    using value_t = std::false_type;
    using type = Default;
};

template<class Default, template<class...> class Op, class... Args>
struct detector<Default, void_t<Op<Args...>>, Op, Args...>
{
    using value_t = std::true_type;
    using type = Op<Args...>;
};

template<template<class...> class Op, class... Args>
using is_detected = typename detector<nonesuch, void, Op, Args...>::value_t;

template<template<class...> class Op, class... Args>
struct is_detected_lazy : is_detected<Op, Args...> { };

template<template<class...> class Op, class... Args>
using detected_t = typename detector<nonesuch, void, Op, Args...>::type;

template<class Default, template<class...> class Op, class... Args>
using detected_or = detector<Default, void, Op, Args...>;

template<class Default, template<class...> class Op, class... Args>
using detected_or_t = typename detected_or<Default, Op, Args...>::type;

template<class Expected, template<class...> class Op, class... Args>
using is_detected_exact = std::is_same<Expected, detected_t<Op, Args...>>;

template<class To, template<class...> class Op, class... Args>
using is_detected_convertible =
    std::is_convertible<detected_t<Op, Args...>, To>;

}  // namespace detail
NLOHMANN_JSON_NAMESPACE_END