assign.hpp

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// Copyright 2024 Ekumen, 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.
 
#ifndef BELUGA_ACTIONS_ASSIGN_HPP
#define BELUGA_ACTIONS_ASSIGN_HPP
 
#include <range/v3/action/action.hpp>
#include <range/v3/functional/bind_back.hpp>
#include <range/v3/range/conversion.hpp>
#include <range/v3/view/view.hpp>
 
namespace beluga::actions {
 
 
template <class T, class = void>
struct is_range_closure : std::false_type {};
 
template <class T>
struct is_range_closure<ranges::actions::action_closure<T>> : std::true_type {};
 
template <class T>
struct is_range_closure<ranges::views::view_closure<T>> : std::true_type {};
 
template <class T>
inline constexpr bool is_range_closure_v = is_range_closure<T>::value;
 
 
namespace detail {
 
struct assign_fn {
  template <
      class Range,
      class Fn,
      std::enable_if_t<ranges::range<Range>, int> = 0,
      std::enable_if_t<is_range_closure_v<Fn>, int> = 0>
  constexpr auto operator()(Range& range, Fn fn) const -> Range& {
    auto&& view = fn(range);
    if constexpr (!std::is_same_v<Range, std::decay_t<decltype(view)>>) {
      // If the result of invoking the closure is not the range itself,
      // then we need to convert the view and assign it to the input range.
      range = std::move(view) | ranges::to<Range>;
    }
    return range;
  }
 
 
  template <class Fn, std::enable_if_t<is_range_closure_v<Fn>, int> = 0>
  friend constexpr auto operator|(Fn fn, assign_fn) {
    return ranges::make_action_closure(ranges::bind_back(assign_fn{}, std::move(fn)));
  }
};
 
}  // namespace detail
 
 
inline constexpr detail::assign_fn assign;
 
}  // namespace beluga::actions
 
#endif