Program Listing for File magic_enum_switch.hpp

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//  __  __             _        ______                          _____
// |  \/  |           (_)      |  ____|                        / ____|_     _
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//                __/ | https://github.com/Neargye/magic_enum
//               |___/  version 0.9.5
//
// Licensed under the MIT License <http://opensource.org/licenses/MIT>.
// SPDX-License-Identifier: MIT
// Copyright (c) 2019 - 2024 Daniil Goncharov <neargye@gmail.com>.
//
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#ifndef NEARGYE_MAGIC_ENUM_SWITCH_HPP
#define NEARGYE_MAGIC_ENUM_SWITCH_HPP

#include "magic_enum.hpp"

namespace magic_enum {

namespace detail {

struct default_result_type {};

template <typename T>
struct identity {
  using type = T;
};

struct nonesuch {};

template <typename F, typename V, bool = std::is_invocable_v<F, V>>
struct invoke_result : identity<nonesuch> {};

template <typename F, typename V>
struct invoke_result<F, V, true> : std::invoke_result<F, V> {};

template <typename F, typename V>
using invoke_result_t = typename invoke_result<F, V>::type;

template <typename E, enum_subtype S, typename F, std::size_t... I>
constexpr auto common_invocable(std::index_sequence<I...>) noexcept {
  static_assert(std::is_enum_v<E>, "magic_enum::detail::invocable_index requires enum type.");

  if constexpr (count_v<E, S> == 0) {
    return identity<nonesuch>{};
  } else {
    return std::common_type<invoke_result_t<F, enum_constant<values_v<E, S>[I]>>...>{};
  }
}

template <typename E, enum_subtype S, typename Result, typename F>
constexpr auto result_type() noexcept {
  static_assert(std::is_enum_v<E>, "magic_enum::detail::result_type requires enum type.");

  constexpr auto seq = std::make_index_sequence<count_v<E, S>>{};
  using R = typename decltype(common_invocable<E, S, F>(seq))::type;
  if constexpr (std::is_same_v<Result, default_result_type>) {
    if constexpr (std::is_same_v<R, nonesuch>) {
      return identity<void>{};
    } else {
      return identity<R>{};
    }
  } else {
    if constexpr (std::is_convertible_v<R, Result>) {
      return identity<Result>{};
    } else if constexpr (std::is_convertible_v<Result, R>) {
      return identity<R>{};
    } else {
      return identity<nonesuch>{};
    }
  }
}

template <typename E, enum_subtype S, typename Result, typename F, typename D = std::decay_t<E>, typename R = typename decltype(result_type<D, S, Result, F>())::type>
using result_t = std::enable_if_t<std::is_enum_v<D> && !std::is_same_v<R, nonesuch>, R>;

#if !defined(MAGIC_ENUM_ENABLE_HASH) && !defined(MAGIC_ENUM_ENABLE_HASH_SWITCH)

template <typename T = void>
inline constexpr auto default_result_type_lambda = []() noexcept(std::is_nothrow_default_constructible_v<T>) { return T{}; };

template <>
inline constexpr auto default_result_type_lambda<void> = []() noexcept {};

template <std::size_t I, std::size_t End, typename R, typename E, enum_subtype S, typename F, typename Def>
constexpr decltype(auto) constexpr_switch_impl(F&& f, E value, Def&& def) {
  if constexpr(I < End) {
    constexpr auto v = enum_constant<enum_value<E, I, S>()>{};
    if (value == v) {
      if constexpr (std::is_invocable_r_v<R, F, decltype(v)>) {
        return static_cast<R>(std::forward<F>(f)(v));
      } else {
        return def();
      }
    } else {
      return constexpr_switch_impl<I + 1, End, R, E, S>(std::forward<F>(f), value, std::forward<Def>(def));
    }
  } else {
    return def();
  }
}

template <typename R, typename E, enum_subtype S, typename F, typename Def>
constexpr decltype(auto) constexpr_switch(F&& f, E value, Def&& def) {
  static_assert(is_enum_v<E>, "magic_enum::detail::constexpr_switch requires enum type.");

  if constexpr (count_v<E, S> == 0) {
    return def();
  } else {
    return constexpr_switch_impl<0, count_v<E, S>, R, E, S>(std::forward<F>(f), value, std::forward<Def>(def));
  }
}
#endif

} // namespace magic_enum::detail

template <typename Result = detail::default_result_type, typename E, detail::enum_subtype S = detail::subtype_v<E>, typename F, typename R = detail::result_t<E, S, Result, F>>
constexpr decltype(auto) enum_switch(F&& f, E value) {
  using D = std::decay_t<E>;
  static_assert(std::is_enum_v<D>, "magic_enum::enum_switch requires enum type.");
  static_assert(detail::is_reflected_v<D, S>, "magic_enum requires enum implementation and valid max and min.");

#if defined(MAGIC_ENUM_ENABLE_HASH) || defined(MAGIC_ENUM_ENABLE_HASH_SWITCH)
  return detail::constexpr_switch<&detail::values_v<D, S>, detail::case_call_t::value>(
      std::forward<F>(f),
      value,
      detail::default_result_type_lambda<R>);
#else
  return detail::constexpr_switch<R, D, S>(
      std::forward<F>(f),
      value,
      detail::default_result_type_lambda<R>);
#endif
}

template <typename Result = detail::default_result_type, detail::enum_subtype S, typename E, typename F, typename R = detail::result_t<E, S, Result, F>>
constexpr decltype(auto) enum_switch(F&& f, E value) {
  return enum_switch<Result, E, S>(std::forward<F>(f), value);
}

template <typename Result, typename E, detail::enum_subtype S = detail::subtype_v<E>, typename F, typename R = detail::result_t<E, S, Result, F>>
constexpr decltype(auto) enum_switch(F&& f, E value, Result&& result) {
  using D = std::decay_t<E>;
  static_assert(std::is_enum_v<D>, "magic_enum::enum_switch requires enum type.");
  static_assert(detail::is_reflected_v<D, S>, "magic_enum requires enum implementation and valid max and min.");

#if defined(MAGIC_ENUM_ENABLE_HASH) || defined(MAGIC_ENUM_ENABLE_HASH_SWITCH)
  return detail::constexpr_switch<&detail::values_v<D, S>, detail::case_call_t::value>(
      std::forward<F>(f),
      value,
      [&result]() -> R { return std::forward<Result>(result); });
#else
  return detail::constexpr_switch<R, D, S>(
      std::forward<F>(f),
      value,
      [&result]() -> R { return std::forward<Result>(result); });
#endif
}

template <typename Result, detail::enum_subtype S, typename E, typename F, typename R = detail::result_t<E, S, Result, F>>
constexpr decltype(auto) enum_switch(F&& f, E value, Result&& result) {
  return enum_switch<Result, E, S>(std::forward<F>(f), value, std::forward<Result>(result));
}

} // namespace magic_enum

template <>
struct std::common_type<magic_enum::detail::nonesuch, magic_enum::detail::nonesuch> : magic_enum::detail::identity<magic_enum::detail::nonesuch> {};

template <typename T>
struct std::common_type<T, magic_enum::detail::nonesuch> : magic_enum::detail::identity<T> {};

template <typename T>
struct std::common_type<magic_enum::detail::nonesuch, T> : magic_enum::detail::identity<T> {};

#endif // NEARGYE_MAGIC_ENUM_SWITCH_HPP