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boost/asio/bind_immediate_executor.hpp

//
// bind_immediate_executor.hpp
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2024 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

#ifndef BOOST_ASIO_BIND_IMMEDIATE_EXECUTOR_HPP
#define BOOST_ASIO_BIND_IMMEDIATE_EXECUTOR_HPP

#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)

#include <boost/asio/detail/config.hpp>
#include <boost/asio/detail/type_traits.hpp>
#include <boost/asio/associated_immediate_executor.hpp>
#include <boost/asio/associator.hpp>
#include <boost/asio/async_result.hpp>

#include <boost/asio/detail/push_options.hpp>

namespace boost {
namespace asio {
namespace detail {

// Helper to automatically define nested typedef result_type.

template <typename T, typename = void>
struct immediate_executor_binder_result_type
{
protected:
  typedef void result_type_or_void;
};

template <typename T>
struct immediate_executor_binder_result_type<T, void_t<typename T::result_type>>
{
  typedef typename T::result_type result_type;
protected:
  typedef result_type result_type_or_void;
};

template <typename R>
struct immediate_executor_binder_result_type<R(*)()>
{
  typedef R result_type;
protected:
  typedef result_type result_type_or_void;
};

template <typename R>
struct immediate_executor_binder_result_type<R(&)()>
{
  typedef R result_type;
protected:
  typedef result_type result_type_or_void;
};

template <typename R, typename A1>
struct immediate_executor_binder_result_type<R(*)(A1)>
{
  typedef R result_type;
protected:
  typedef result_type result_type_or_void;
};

template <typename R, typename A1>
struct immediate_executor_binder_result_type<R(&)(A1)>
{
  typedef R result_type;
protected:
  typedef result_type result_type_or_void;
};

template <typename R, typename A1, typename A2>
struct immediate_executor_binder_result_type<R(*)(A1, A2)>
{
  typedef R result_type;
protected:
  typedef result_type result_type_or_void;
};

template <typename R, typename A1, typename A2>
struct immediate_executor_binder_result_type<R(&)(A1, A2)>
{
  typedef R result_type;
protected:
  typedef result_type result_type_or_void;
};

// Helper to automatically define nested typedef argument_type.

template <typename T, typename = void>
struct immediate_executor_binder_argument_type {};

template <typename T>
struct immediate_executor_binder_argument_type<T,
  void_t<typename T::argument_type>>
{
  typedef typename T::argument_type argument_type;
};

template <typename R, typename A1>
struct immediate_executor_binder_argument_type<R(*)(A1)>
{
  typedef A1 argument_type;
};

template <typename R, typename A1>
struct immediate_executor_binder_argument_type<R(&)(A1)>
{
  typedef A1 argument_type;
};

// Helper to automatically define nested typedefs first_argument_type and
// second_argument_type.

template <typename T, typename = void>
struct immediate_executor_binder_argument_types {};

template <typename T>
struct immediate_executor_binder_argument_types<T,
  void_t<typename T::first_argument_type>>
{
  typedef typename T::first_argument_type first_argument_type;
  typedef typename T::second_argument_type second_argument_type;
};

template <typename R, typename A1, typename A2>
struct immediate_executor_binder_argument_type<R(*)(A1, A2)>
{
  typedef A1 first_argument_type;
  typedef A2 second_argument_type;
};

template <typename R, typename A1, typename A2>
struct immediate_executor_binder_argument_type<R(&)(A1, A2)>
{
  typedef A1 first_argument_type;
  typedef A2 second_argument_type;
};

} // namespace detail

/// A call wrapper type to bind a immediate executor of type @c Executor
/// to an object of type @c T.
template <typename T, typename Executor>
class immediate_executor_binder
#if !defined(GENERATING_DOCUMENTATION)
  : public detail::immediate_executor_binder_result_type<T>,
    public detail::immediate_executor_binder_argument_type<T>,
    public detail::immediate_executor_binder_argument_types<T>
#endif // !defined(GENERATING_DOCUMENTATION)
{
public:
  /// The type of the target object.
  typedef T target_type;

  /// The type of the associated immediate executor.
  typedef Executor immediate_executor_type;

#if defined(GENERATING_DOCUMENTATION)
  /// The return type if a function.
  /**
   * The type of @c result_type is based on the type @c T of the wrapper's
   * target object:
   *
   * @li if @c T is a pointer to function type, @c result_type is a synonym for
   * the return type of @c T;
   *
   * @li if @c T is a class type with a member type @c result_type, then @c
   * result_type is a synonym for @c T::result_type;
   *
   * @li otherwise @c result_type is not defined.
   */
  typedef see_below result_type;

  /// The type of the function's argument.
  /**
   * The type of @c argument_type is based on the type @c T of the wrapper's
   * target object:
   *
   * @li if @c T is a pointer to a function type accepting a single argument,
   * @c argument_type is a synonym for the return type of @c T;
   *
   * @li if @c T is a class type with a member type @c argument_type, then @c
   * argument_type is a synonym for @c T::argument_type;
   *
   * @li otherwise @c argument_type is not defined.
   */
  typedef see_below argument_type;

  /// The type of the function's first argument.
  /**
   * The type of @c first_argument_type is based on the type @c T of the
   * wrapper's target object:
   *
   * @li if @c T is a pointer to a function type accepting two arguments, @c
   * first_argument_type is a synonym for the return type of @c T;
   *
   * @li if @c T is a class type with a member type @c first_argument_type,
   * then @c first_argument_type is a synonym for @c T::first_argument_type;
   *
   * @li otherwise @c first_argument_type is not defined.
   */
  typedef see_below first_argument_type;

  /// The type of the function's second argument.
  /**
   * The type of @c second_argument_type is based on the type @c T of the
   * wrapper's target object:
   *
   * @li if @c T is a pointer to a function type accepting two arguments, @c
   * second_argument_type is a synonym for the return type of @c T;
   *
   * @li if @c T is a class type with a member type @c first_argument_type,
   * then @c second_argument_type is a synonym for @c T::second_argument_type;
   *
   * @li otherwise @c second_argument_type is not defined.
   */
  typedef see_below second_argument_type;
#endif // defined(GENERATING_DOCUMENTATION)

  /// Construct a immediate executor wrapper for the specified object.
  /**
   * This constructor is only valid if the type @c T is constructible from type
   * @c U.
   */
  template <typename U>
  immediate_executor_binder(const immediate_executor_type& e,
      U&& u)
    : executor_(e),
      target_(static_cast<U&&>(u))
  {
  }

  /// Copy constructor.
  immediate_executor_binder(const immediate_executor_binder& other)
    : executor_(other.get_immediate_executor()),
      target_(other.get())
  {
  }

  /// Construct a copy, but specify a different immediate executor.
  immediate_executor_binder(const immediate_executor_type& e,
      const immediate_executor_binder& other)
    : executor_(e),
      target_(other.get())
  {
  }

  /// Construct a copy of a different immediate executor wrapper type.
  /**
   * This constructor is only valid if the @c Executor type is
   * constructible from type @c OtherExecutor, and the type @c T is
   * constructible from type @c U.
   */
  template <typename U, typename OtherExecutor>
  immediate_executor_binder(
      const immediate_executor_binder<U, OtherExecutor>& other,
      constraint_t<is_constructible<Executor, OtherExecutor>::value> = 0,
      constraint_t<is_constructible<T, U>::value> = 0)
    : executor_(other.get_immediate_executor()),
      target_(other.get())
  {
  }

  /// Construct a copy of a different immediate executor wrapper type, but
  /// specify a different immediate executor.
  /**
   * This constructor is only valid if the type @c T is constructible from type
   * @c U.
   */
  template <typename U, typename OtherExecutor>
  immediate_executor_binder(const immediate_executor_type& e,
      const immediate_executor_binder<U, OtherExecutor>& other,
      constraint_t<is_constructible<T, U>::value> = 0)
    : executor_(e),
      target_(other.get())
  {
  }

  /// Move constructor.
  immediate_executor_binder(immediate_executor_binder&& other)
    : executor_(static_cast<immediate_executor_type&&>(
          other.get_immediate_executor())),
      target_(static_cast<T&&>(other.get()))
  {
  }

  /// Move construct the target object, but specify a different immediate
  /// executor.
  immediate_executor_binder(const immediate_executor_type& e,
      immediate_executor_binder&& other)
    : executor_(e),
      target_(static_cast<T&&>(other.get()))
  {
  }

  /// Move construct from a different immediate executor wrapper type.
  template <typename U, typename OtherExecutor>
  immediate_executor_binder(
      immediate_executor_binder<U, OtherExecutor>&& other,
      constraint_t<is_constructible<Executor, OtherExecutor>::value> = 0,
      constraint_t<is_constructible<T, U>::value> = 0)
    : executor_(static_cast<OtherExecutor&&>(
          other.get_immediate_executor())),
      target_(static_cast<U&&>(other.get()))
  {
  }

  /// Move construct from a different immediate executor wrapper type, but
  /// specify a different immediate executor.
  template <typename U, typename OtherExecutor>
  immediate_executor_binder(const immediate_executor_type& e,
      immediate_executor_binder<U, OtherExecutor>&& other,
      constraint_t<is_constructible<T, U>::value> = 0)
    : executor_(e),
      target_(static_cast<U&&>(other.get()))
  {
  }

  /// Destructor.
  ~immediate_executor_binder()
  {
  }

  /// Obtain a reference to the target object.
  target_type& get() noexcept
  {
    return target_;
  }

  /// Obtain a reference to the target object.
  const target_type& get() const noexcept
  {
    return target_;
  }

  /// Obtain the associated immediate executor.
  immediate_executor_type get_immediate_executor() const noexcept
  {
    return executor_;
  }

  /// Forwarding function call operator.
  template <typename... Args>
  result_of_t<T(Args...)> operator()(Args&&... args)
  {
    return target_(static_cast<Args&&>(args)...);
  }

  /// Forwarding function call operator.
  template <typename... Args>
  result_of_t<T(Args...)> operator()(Args&&... args) const
  {
    return target_(static_cast<Args&&>(args)...);
  }

private:
  Executor executor_;
  T target_;
};

/// Associate an object of type @c T with a immediate executor of type
/// @c Executor.
template <typename Executor, typename T>
BOOST_ASIO_NODISCARD inline immediate_executor_binder<decay_t<T>, Executor>
bind_immediate_executor(const Executor& e, T&& t)
{
  return immediate_executor_binder<
    decay_t<T>, Executor>(
      e, static_cast<T&&>(t));
}

#if !defined(GENERATING_DOCUMENTATION)

namespace detail {

template <typename TargetAsyncResult, typename Executor, typename = void>
class immediate_executor_binder_completion_handler_async_result
{
public:
  template <typename T>
  explicit immediate_executor_binder_completion_handler_async_result(T&)
  {
  }
};

template <typename TargetAsyncResult, typename Executor>
class immediate_executor_binder_completion_handler_async_result<
  TargetAsyncResult, Executor,
  void_t<
    typename TargetAsyncResult::completion_handler_type
  >>
{
private:
  TargetAsyncResult target_;

public:
  typedef immediate_executor_binder<
    typename TargetAsyncResult::completion_handler_type, Executor>
      completion_handler_type;

  explicit immediate_executor_binder_completion_handler_async_result(
      typename TargetAsyncResult::completion_handler_type& handler)
    : target_(handler)
  {
  }

  auto get() -> decltype(target_.get())
  {
    return target_.get();
  }
};

template <typename TargetAsyncResult, typename = void>
struct immediate_executor_binder_async_result_return_type
{
};

template <typename TargetAsyncResult>
struct immediate_executor_binder_async_result_return_type<
  TargetAsyncResult,
  void_t<
    typename TargetAsyncResult::return_type
  >>
{
  typedef typename TargetAsyncResult::return_type return_type;
};

} // namespace detail

template <typename T, typename Executor, typename Signature>
class async_result<immediate_executor_binder<T, Executor>, Signature> :
  public detail::immediate_executor_binder_completion_handler_async_result<
    async_result<T, Signature>, Executor>,
  public detail::immediate_executor_binder_async_result_return_type<
    async_result<T, Signature>>
{
public:
  explicit async_result(immediate_executor_binder<T, Executor>& b)
    : detail::immediate_executor_binder_completion_handler_async_result<
        async_result<T, Signature>, Executor>(b.get())
  {
  }

  template <typename Initiation>
  struct init_wrapper
  {
    template <typename Init>
    init_wrapper(const Executor& e, Init&& init)
      : executor_(e),
        initiation_(static_cast<Init&&>(init))
    {
    }

    template <typename Handler, typename... Args>
    void operator()(Handler&& handler, Args&&... args)
    {
      static_cast<Initiation&&>(initiation_)(
          immediate_executor_binder<
            decay_t<Handler>, Executor>(
              executor_, static_cast<Handler&&>(handler)),
          static_cast<Args&&>(args)...);
    }

    template <typename Handler, typename... Args>
    void operator()(Handler&& handler, Args&&... args) const
    {
      initiation_(
          immediate_executor_binder<
            decay_t<Handler>, Executor>(
              executor_, static_cast<Handler&&>(handler)),
          static_cast<Args&&>(args)...);
    }

    Executor executor_;
    Initiation initiation_;
  };

  template <typename Initiation, typename RawCompletionToken, typename... Args>
  static auto initiate(Initiation&& initiation,
      RawCompletionToken&& token, Args&&... args)
    -> decltype(
      async_initiate<T, Signature>(
        declval<init_wrapper<decay_t<Initiation>>>(),
        token.get(), static_cast<Args&&>(args)...))
  {
    return async_initiate<T, Signature>(
        init_wrapper<decay_t<Initiation>>(
          token.get_immediate_executor(),
          static_cast<Initiation&&>(initiation)),
        token.get(), static_cast<Args&&>(args)...);
  }

private:
  async_result(const async_result&) = delete;
  async_result& operator=(const async_result&) = delete;

  async_result<T, Signature> target_;
};

template <template <typename, typename> class Associator,
    typename T, typename Executor, typename DefaultCandidate>
struct associator<Associator,
    immediate_executor_binder<T, Executor>,
    DefaultCandidate>
  : Associator<T, DefaultCandidate>
{
  static typename Associator<T, DefaultCandidate>::type get(
      const immediate_executor_binder<T, Executor>& b) noexcept
  {
    return Associator<T, DefaultCandidate>::get(b.get());
  }

  static auto get(const immediate_executor_binder<T, Executor>& b,
      const DefaultCandidate& c) noexcept
    -> decltype(Associator<T, DefaultCandidate>::get(b.get(), c))
  {
    return Associator<T, DefaultCandidate>::get(b.get(), c);
  }
};

template <typename T, typename Executor, typename Executor1>
struct associated_immediate_executor<
    immediate_executor_binder<T, Executor>,
    Executor1>
{
  typedef Executor type;

  static auto get(const immediate_executor_binder<T, Executor>& b,
      const Executor1& = Executor1()) noexcept
    -> decltype(b.get_immediate_executor())
  {
    return b.get_immediate_executor();
  }
};

#endif // !defined(GENERATING_DOCUMENTATION)

} // namespace asio
} // namespace boost

#include <boost/asio/detail/pop_options.hpp>

#endif // BOOST_ASIO_BIND_IMMEDIATE_EXECUTOR_HPP