include/unifex/just.hpp

/*
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * Licensed under the Apache License Version 2.0 with LLVM Exceptions
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *   https://llvm.org/LICENSE.txt
 *
 * 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 <unifex/config.hpp>
#include <unifex/receiver_concepts.hpp>
#include <unifex/sender_concepts.hpp>
#include <unifex/blocking.hpp>
#include <unifex/std_concepts.hpp>

#include <exception>
#include <tuple>
#include <type_traits>
#include <utility>

#include <unifex/detail/prologue.hpp>

namespace unifex {
namespace _just {

template <typename Receiver, typename... Values>
struct _op {
  struct type;
};
template <typename Receiver, typename... Values>
using operation = typename _op<remove_cvref_t<Receiver>, Values...>::type;

template <typename Receiver, typename... Values>
struct _op<Receiver, Values...>::type {
  UNIFEX_NO_UNIQUE_ADDRESS std::tuple<Values...> values_;
  UNIFEX_NO_UNIQUE_ADDRESS Receiver receiver_;

  void start() & noexcept {
    UNIFEX_TRY {
      std::apply(
          [&](Values&&... values) {
            unifex::set_value((Receiver &&) receiver_, (Values &&) values...);
          },
          std::move(values_));
    } UNIFEX_CATCH (...) {
      unifex::set_error((Receiver &&) receiver_, std::current_exception());
    }
  }
};

template <typename... Values>
struct _sender {
  class type;
};
template <typename... Values>
using sender = typename _sender<std::decay_t<Values>...>::type;

template <typename... Values>
class _sender<Values...>::type {
  UNIFEX_NO_UNIQUE_ADDRESS std::tuple<Values...> values_;

  public:
  template <
      template <typename...> class Variant,
      template <typename...> class Tuple>
  using value_types = Variant<Tuple<Values...>>;

  template <template <typename...> class Variant>
  using error_types = Variant<std::exception_ptr>;

  static constexpr bool sends_done = false;

  template(typename... Values2)
    (requires (sizeof...(Values2) == sizeof...(Values)) AND
      constructible_from<std::tuple<Values...>, Values2...>)
  explicit type(std::in_place_t, Values2&&... values)
    noexcept(std::is_nothrow_constructible_v<std::tuple<Values...>, Values2...>)
    : values_((Values2 &&) values...) {}

  template(typename This, typename Receiver)
      (requires same_as<remove_cvref_t<This>, type> AND
        receiver<Receiver> AND
        constructible_from<std::tuple<Values...>, member_t<This, std::tuple<Values...>>>)
  friend auto tag_invoke(tag_t<connect>, This&& that, Receiver&& r)
      noexcept(std::is_nothrow_constructible_v<std::tuple<Values...>, member_t<This, std::tuple<Values...>>>)
      -> operation<Receiver, Values...> {
    return {static_cast<This&&>(that).values_, static_cast<Receiver&&>(r)};
  }

  friend constexpr blocking_kind tag_invoke(tag_t<blocking>, const type&) noexcept {
    return blocking_kind::always_inline;
  }
};
} // namespace _just

namespace _just_cpo {
  inline const struct just_fn {
    template <typename... Values>
    constexpr auto operator()(Values&&... values) const
      noexcept(std::is_nothrow_constructible_v<_just::sender<Values...>, std::in_place_t, Values...>)
      -> _just::sender<Values...> {
      return _just::sender<Values...>{std::in_place, (Values&&)values...};
    }
  } just{};
} // namespace _just_cpo
using _just_cpo::just;

} // namespace unifex

#include <unifex/detail/epilogue.hpp>