fold.hpp

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// Copyright 2015 TIER IV, Inc. All rights reserved.
//
// 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 OPENSCENARIO_INTERPRETER__FUNCTIONAL__FOLD_HPP_
#define OPENSCENARIO_INTERPRETER__FUNCTIONAL__FOLD_HPP_
 
#include <functional>
#include <utility>
 
namespace openscenario_interpreter
{
inline namespace functional
{
template <typename F, typename T>
constexpr decltype(auto) fold_left(F &&, T && x)
{
  return std::forward<decltype(x)>(x);
}
 
template <typename F, typename T, typename U, typename... Ts>
constexpr decltype(auto) fold_left(F && f, T && x, U && y, Ts &&... xs)
{
  return fold_left(
    f, f(std::forward<decltype(x)>(x), std::forward<decltype(y)>(y)),
    std::forward<decltype(xs)>(xs)...);
}
 
template <typename F, typename T>
constexpr decltype(auto) fold_right(F &&, T && x)
{
  return std::forward<decltype(x)>(x);
}
 
template <typename F, typename T, typename... Ts>
constexpr decltype(auto) fold_right(F && f, T && x, Ts &&... xs)
{
  return f(std::forward<decltype(x)>(x), fold_right(f, std::forward<decltype(xs)>(xs)...));
}
 
template <typename... Ts>
constexpr auto fold(Ts &&... xs) -> decltype(auto)
{
  return fold_left(std::forward<decltype(xs)>(xs)...);
}
}  // namespace functional
}  // namespace openscenario_interpreter
 
#endif  // OPENSCENARIO_INTERPRETER__FUNCTIONAL__FOLD_HPP_