ApplyTuple.h

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/*
 * Copyright 2012-present Facebook, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#pragma once

#include <functional>
#include <tuple>
#include <utility>

#include <folly/Traits.h>
#include <folly/Utility.h>
#include <folly/functional/Invoke.h>

namespace folly {


template <typename Tuple>
using index_sequence_for_tuple =
    make_index_sequence<std::tuple_size<Tuple>::value>;

namespace detail {
namespace apply_tuple {
namespace adl {
using std::get;

struct ApplyInvoke {
  template <typename T>
  using seq = index_sequence_for_tuple<std::remove_reference_t<T>>;

  template <typename F, typename T, std::size_t... I>
  static constexpr auto invoke_(F&& f, T&& t, index_sequence<I...>) noexcept(
      is_nothrow_invocable<F&&, decltype(get<I>(std::declval<T>()))...>::value)
      -> invoke_result_t<F&&, decltype(get<I>(std::declval<T>()))...> {
    return invoke(static_cast<F&&>(f), get<I>(static_cast<T&&>(t))...);
  }
};

template <
    typename Tuple,
    std::size_t... Indices,
    typename ReturnTuple =
        std::tuple<decltype(get<Indices>(std::declval<Tuple>()))...>>
auto forward_tuple(Tuple&& tuple, index_sequence<Indices...>) -> ReturnTuple {
  return ReturnTuple{get<Indices>(std::forward<Tuple>(tuple))...};
}
} // namespace adl
} // namespace apply_tuple
} // namespace detail

struct ApplyInvoke : private detail::apply_tuple::adl::ApplyInvoke {
 public:
  template <typename F, typename T>
  constexpr auto operator()(F&& f, T&& t) const noexcept(
      noexcept(invoke_(static_cast<F&&>(f), static_cast<T&&>(t), seq<T>{})))
      -> decltype(invoke_(static_cast<F&&>(f), static_cast<T&&>(t), seq<T>{})) {
    return invoke_(static_cast<F&&>(f), static_cast<T&&>(t), seq<T>{});
  }
};


#if __cpp_lib_apply >= 201603

/* using override */ using std::apply;

#else // __cpp_lib_apply >= 201603

//  mimic: std::apply, C++17
template <typename F, typename Tuple>
constexpr decltype(auto) apply(F&& func, Tuple&& tuple) {
  return ApplyInvoke{}(static_cast<F&&>(func), static_cast<Tuple&&>(tuple));
}

#endif // __cpp_lib_apply >= 201603

template <typename Tuple>
auto forward_tuple(Tuple&& tuple) noexcept
    -> decltype(detail::apply_tuple::adl::forward_tuple(
        std::declval<Tuple>(),
        std::declval<
            index_sequence_for_tuple<std::remove_reference_t<Tuple>>>())) {
  return detail::apply_tuple::adl::forward_tuple(
      std::forward<Tuple>(tuple),
      index_sequence_for_tuple<std::remove_reference_t<Tuple>>{});
}

template <typename F, typename Tuple>
struct apply_result : invoke_result<ApplyInvoke, F, Tuple> {};
template <typename F, typename Tuple>
using apply_result_t = invoke_result_t<ApplyInvoke, F, Tuple>;
template <typename F, typename Tuple>
struct is_applicable : is_invocable<ApplyInvoke, F, Tuple> {};
template <typename R, typename F, typename Tuple>
struct is_applicable_r : is_invocable_r<R, ApplyInvoke, F, Tuple> {};
template <typename F, typename Tuple>
struct is_nothrow_applicable : is_nothrow_invocable<ApplyInvoke, F, Tuple> {};
template <typename R, typename F, typename Tuple>
struct is_nothrow_applicable_r
    : is_nothrow_invocable_r<R, ApplyInvoke, F, Tuple> {};

namespace detail {
namespace apply_tuple {

template <class F>
class Uncurry {
 public:
  explicit Uncurry(F&& func) : func_(std::move(func)) {}
  explicit Uncurry(const F& func) : func_(func) {}

  template <class Tuple>
  auto operator()(Tuple&& tuple) const
      -> decltype(apply(std::declval<F>(), std::forward<Tuple>(tuple))) {
    return apply(func_, std::forward<Tuple>(tuple));
  }

 private:
  F func_;
};
} // namespace apply_tuple
} // namespace detail

template <class F>
auto uncurry(F&& f)
    -> detail::apply_tuple::Uncurry<typename std::decay<F>::type> {
  return detail::apply_tuple::Uncurry<typename std::decay<F>::type>(
      std::forward<F>(f));
}

#if __cpp_lib_make_from_tuple || (_MSC_VER >= 1910 && _MSVC_LANG > 201402)

/* using override */ using std::make_from_tuple;

#else

namespace detail {
namespace apply_tuple {
template <class T>
struct Construct {
  template <class... Args>
  constexpr T operator()(Args&&... args) const {
    return T(std::forward<Args>(args)...);
  }
};
} // namespace apply_tuple
} // namespace detail

//  mimic: std::make_from_tuple, C++17
template <class T, class Tuple>
constexpr T make_from_tuple(Tuple&& t) {
  return apply(detail::apply_tuple::Construct<T>(), std::forward<Tuple>(t));
}

#endif

} // namespace folly