unique_resource.hpp

// unique_resource
// Copyright (c) 2015 okdshin
// Portions Copyright (c) 2020 D3 Engineering, LLC.
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
// This implementation is based on C++ standards committee paper N4189.
#ifndef UNIQUE_RESOURCE_H_
#define UNIQUE_RESOURCE_H_
#include <utility>
// workaround for GCC
#if defined(__GNUC__)
#ifdef UNIQUE_RESOURCE_ALLOW_DELETER_CALL_THROWING_EXCEPTION
#define UNIQUE_RESOURCE_NOEXCEPT
#else
#define UNIQUE_RESOURCE_NOEXCEPT noexcept
#endif
#define UNIQUE_RESOURCE_NOEXCEPT_NOEXCEPT_THIS_RESET UNIQUE_RESOURCE_NOEXCEPT
#define UNIQUE_RESOURCE_NOEXCEPT_NOEXCEPT_THIS_DELETER_CALL                    \
  UNIQUE_RESOURCE_NOEXCEPT
#else
#define UNIQUE_RESOURCE_NOEXCEPT_NOEXCEPT_THIS_RESET                           \
  noexcept(noexcept(this->reset()))
#define UNIQUE_RESOURCE_NOEXCEPT_NOEXCEPT_THIS_DELETER_CALL                    \
  noexcept(noexcept(this->get_deleter()(resource)))
#endif
namespace std_experimental {

// By Herb Sutter, <https://herbsutter.com/gotw/_102/>.
// Copied here since C++11 doesn't have std::make_unique().
template<typename T, typename ...Args>
std::unique_ptr<T> make_unique( Args&& ...args )
{
    return std::unique_ptr<T>( new T( std::forward<Args>(args)... ) );
}

template <typename R, typename D> class unique_resource {
  R resource;
  D deleter;
  bool execute_on_destruction; // exposition only
  unique_resource &operator=(unique_resource const &) = delete;
  unique_resource(unique_resource const &) = delete; // no copies!
public:
  // construction
  explicit unique_resource(R &&resource_, D &&deleter_,
                           bool shouldrun = true) noexcept
      : resource(std::move(resource_)),
        deleter(std::move(deleter_)),
        execute_on_destruction{shouldrun} {}
  // move
  unique_resource(unique_resource &&other) noexcept
      : resource(std::move(other.resource)),
        deleter(std::move(other.deleter)),
        execute_on_destruction{other.execute_on_destruction} {
    other.release();
  }
  unique_resource &operator=(unique_resource &&other)
      UNIQUE_RESOURCE_NOEXCEPT_NOEXCEPT_THIS_RESET {
    this->reset();
    this->deleter = std::move(other.deleter);
    this->resource = std::move(other.resource);
    this->execute_on_destruction = other.execute_on_destruction;
    other.release();
    return *this;
  }
  // resource release
  ~unique_resource() UNIQUE_RESOURCE_NOEXCEPT_NOEXCEPT_THIS_RESET {
    this->reset();
  }
  void reset() UNIQUE_RESOURCE_NOEXCEPT_NOEXCEPT_THIS_DELETER_CALL {
    if (execute_on_destruction) {
      this->execute_on_destruction = false;
      this->get_deleter()(resource);
    }
  }
  void reset(R &&newresource) UNIQUE_RESOURCE_NOEXCEPT_NOEXCEPT_THIS_RESET {
    this->reset();
    this->resource = std::move(newresource);
    this->execute_on_destruction = true;
  }
  R const &release() noexcept {
    this->execute_on_destruction = false;
    return this->get();
  }
  // resource access
  R const &get() const noexcept { return this->resource; }
  operator R const &() const noexcept { return this->resource; }
  R operator->() const noexcept { return this->resource; }
  typename std::add_lvalue_reference<
      typename std::remove_pointer<R>::type>::type
  operator*() const {
    return *this->resource;
  }
  // deleter access
  const D &get_deleter() const noexcept { return this->deleter; }
};
// factories
template <typename R, typename D>
unique_resource<R, typename std::remove_reference<D>::type>
make_unique_resource(R &&r, D &&d) noexcept {
  return unique_resource<R, typename std::remove_reference<D>::type>(
      std::move(r), std::forward<typename std::remove_reference<D>::type>(d),
      true);
}
template <typename R, typename D>
unique_resource<R, D> make_unique_resource_checked(R r, R invalid,
                                                   D d) noexcept {
  bool shouldrun = not bool(r == invalid);
  return unique_resource<R, D>(std::move(r), std::move(d), shouldrun);
}
}
#endif /* UNIQUE_RESOURCE_H_ */