text: //
  // impl/compose.hpp
  // ~~~~~~~~~~~~~~~~
  //
  // Copyright (c) 2003-2019 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_IMPL_COMPOSE_HPP
  #define BOOST_ASIO_IMPL_COMPOSE_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/handler_alloc_helpers.hpp>
  #include <boost/asio/detail/handler_cont_helpers.hpp>
  #include <boost/asio/detail/handler_invoke_helpers.hpp>
  #include <boost/asio/detail/type_traits.hpp>
  #include <boost/asio/detail/variadic_templates.hpp>
  #include <boost/asio/executor_work_guard.hpp>
  #include <boost/asio/is_executor.hpp>
  #include <boost/asio/system_executor.hpp>
  
  #include <boost/asio/detail/push_options.hpp>
  
  namespace boost {
  namespace asio {
  
  namespace detail
  {
    template <typename>
    struct composed_io_executors;
  
    template <>
    struct composed_io_executors<void()>
    {
      composed_io_executors() BOOST_ASIO_NOEXCEPT
        : head_(system_executor())
      {
      }
  
      typedef system_executor head_type;
      system_executor head_;
    };
  
    inline composed_io_executors<void()> make_composed_io_executors()
    {
      return composed_io_executors<void()>();
    }
  
    template <typename Head>
    struct composed_io_executors<void(Head)>
    {
      explicit composed_io_executors(const Head& ex) BOOST_ASIO_NOEXCEPT
        : head_(ex)
      {
      }
  
      typedef Head head_type;
      Head head_;
    };
  
    template <typename Head>
    inline composed_io_executors<void(Head)>
    make_composed_io_executors(const Head& head)
    {
      return composed_io_executors<void(Head)>(head);
    }
  
  #if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
  
    template <typename Head, typename... Tail>
    struct composed_io_executors<void(Head, Tail...)>
    {
      explicit composed_io_executors(const Head& head,
          const Tail&... tail) BOOST_ASIO_NOEXCEPT
        : head_(head),
          tail_(tail...)
      {
      }
  
      void reset()
      {
        head_.reset();
        tail_.reset();
      }
  
      typedef Head head_type;
      Head head_;
      composed_io_executors<void(Tail...)> tail_;
    };
  
    template <typename Head, typename... Tail>
    inline composed_io_executors<void(Head, Tail...)>
    make_composed_io_executors(const Head& head, const Tail&... tail)
    {
      return composed_io_executors<void(Head, Tail...)>(head, tail...);
    }
  
  #else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
  
  #define BOOST_ASIO_PRIVATE_COMPOSED_IO_EXECUTORS_DEF(n) \
    template <typename Head, BOOST_ASIO_VARIADIC_TPARAMS(n)> \
    struct composed_io_executors<void(Head, BOOST_ASIO_VARIADIC_TARGS(n))> \
    { \
      explicit composed_io_executors(const Head& head, \
          BOOST_ASIO_VARIADIC_CONSTREF_PARAMS(n)) BOOST_ASIO_NOEXCEPT \
        : head_(head), \
          tail_(BOOST_ASIO_VARIADIC_BYVAL_ARGS(n)) \
      { \
      } \
    \
      void reset() \
      { \
        head_.reset(); \
        tail_.reset(); \
      } \
    \
      typedef Head head_type; \
      Head head_; \
      composed_io_executors<void(BOOST_ASIO_VARIADIC_TARGS(n))> tail_; \
    }; \
    \
    template <typename Head, BOOST_ASIO_VARIADIC_TPARAMS(n)> \
    inline composed_io_executors<void(Head, BOOST_ASIO_VARIADIC_TARGS(n))> \
    make_composed_io_executors(const Head& head, \
        BOOST_ASIO_VARIADIC_CONSTREF_PARAMS(n)) \
    { \
      return composed_io_executors< \
        void(Head, BOOST_ASIO_VARIADIC_TARGS(n))>( \
          head, BOOST_ASIO_VARIADIC_BYVAL_ARGS(n)); \
    } \
    /**/
    BOOST_ASIO_VARIADIC_GENERATE(BOOST_ASIO_PRIVATE_COMPOSED_IO_EXECUTORS_DEF)
  #undef BOOST_ASIO_PRIVATE_COMPOSED_IO_EXECUTORS_DEF
  
  #endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
  
    template <typename>
    struct composed_work;
  
    template <>
    struct composed_work<void()>
    {
      typedef composed_io_executors<void()> executors_type;
  
      composed_work(const executors_type&) BOOST_ASIO_NOEXCEPT
        : head_(system_executor())
      {
      }
  
      void reset()
      {
        head_.reset();
      }
  
      typedef system_executor head_type;
      executor_work_guard<system_executor> head_;
    };
  
    template <typename Head>
    struct composed_work<void(Head)>
    {
      typedef composed_io_executors<void(Head)> executors_type;
  
      explicit composed_work(const executors_type& ex) BOOST_ASIO_NOEXCEPT
        : head_(ex.head_)
      {
      }
  
      void reset()
      {
        head_.reset();
      }
  
      typedef Head head_type;
      executor_work_guard<Head> head_;
    };
  
  #if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
  
    template <typename Head, typename... Tail>
    struct composed_work<void(Head, Tail...)>
    {
      typedef composed_io_executors<void(Head, Tail...)> executors_type;
  
      explicit composed_work(const executors_type& ex) BOOST_ASIO_NOEXCEPT
        : head_(ex.head_),
          tail_(ex.tail_)
      {
      }
  
      void reset()
      {
        head_.reset();
        tail_.reset();
      }
  
      typedef Head head_type;
      executor_work_guard<Head> head_;
      composed_work<void(Tail...)> tail_;
    };
  
  #else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
  
  #define BOOST_ASIO_PRIVATE_COMPOSED_WORK_DEF(n) \
    template <typename Head, BOOST_ASIO_VARIADIC_TPARAMS(n)> \
    struct composed_work<void(Head, BOOST_ASIO_VARIADIC_TARGS(n))> \
    { \
      typedef composed_io_executors<void(Head, \
        BOOST_ASIO_VARIADIC_TARGS(n))> executors_type; \
    \
      explicit composed_work(const executors_type& ex) BOOST_ASIO_NOEXCEPT \
        : head_(ex.head_), \
          tail_(ex.tail_) \
      { \
      } \
    \
      void reset() \
      { \
        head_.reset(); \
        tail_.reset(); \
      } \
    \
      typedef Head head_type; \
      executor_work_guard<Head> head_; \
      composed_work<void(BOOST_ASIO_VARIADIC_TARGS(n))> tail_; \
    }; \
    /**/
    BOOST_ASIO_VARIADIC_GENERATE(BOOST_ASIO_PRIVATE_COMPOSED_WORK_DEF)
  #undef BOOST_ASIO_PRIVATE_COMPOSED_WORK_DEF
  
  #endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
  
  #if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
    template <typename Impl, typename Work, typename Handler, typename Signature>
    class composed_op;
  
    template <typename Impl, typename Work, typename Handler,
        typename R, typename... Args>
    class composed_op<Impl, Work, Handler, R(Args...)>
  #else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
    template <typename Impl, typename Work, typename Handler, typename Signature>
    class composed_op
  #endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
    {
    public:
      composed_op(BOOST_ASIO_MOVE_ARG(Impl) impl,
          BOOST_ASIO_MOVE_ARG(Work) work,
          BOOST_ASIO_MOVE_ARG(Handler) handler)
        : impl_(BOOST_ASIO_MOVE_CAST(Impl)(impl)),
          work_(BOOST_ASIO_MOVE_CAST(Work)(work)),
          handler_(BOOST_ASIO_MOVE_CAST(Handler)(handler)),
          invocations_(0)
      {
      }
  
  #if defined(BOOST_ASIO_HAS_MOVE)
      composed_op(composed_op&& other)
        : impl_(BOOST_ASIO_MOVE_CAST(Impl)(other.impl_)),
          work_(BOOST_ASIO_MOVE_CAST(Work)(other.work_)),
          handler_(BOOST_ASIO_MOVE_CAST(Handler)(other.handler_)),
          invocations_(other.invocations_)
      {
      }
  #endif // defined(BOOST_ASIO_HAS_MOVE)
  
      typedef typename associated_executor<Handler,
          typename Work::head_type>::type executor_type;
  
      executor_type get_executor() const BOOST_ASIO_NOEXCEPT
      {
        return (get_associated_executor)(handler_, work_.head_.get_executor());
      }
  
      typedef typename associated_allocator<Handler,
        std::allocator<void> >::type allocator_type;
  
      allocator_type get_allocator() const BOOST_ASIO_NOEXCEPT
      {
        return (get_associated_allocator)(handler_, std::allocator<void>());
      }
  
  #if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
  
      template<typename... T>
      void operator()(BOOST_ASIO_MOVE_ARG(T)... t)
      {
        if (invocations_ < ~unsigned(0))
          ++invocations_;
        impl_(*this, BOOST_ASIO_MOVE_CAST(T)(t)...);
      }
  
      void complete(Args... args)
      {
        this->work_.reset();
        this->handler_(BOOST_ASIO_MOVE_CAST(Args)(args)...);
      }
  
  #else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
  
      void operator()()
      {
        if (invocations_ < ~unsigned(0))
          ++invocations_;
        impl_(*this);
      }
  
      void complete()
      {
        this->work_.reset();
        this->handler_();
      }
  
  #define BOOST_ASIO_PRIVATE_COMPOSED_OP_DEF(n) \
      template<BOOST_ASIO_VARIADIC_TPARAMS(n)> \
      void operator()(BOOST_ASIO_VARIADIC_MOVE_PARAMS(n)) \
      { \
        if (invocations_ < ~unsigned(0)) \
          ++invocations_; \
        impl_(*this, BOOST_ASIO_VARIADIC_MOVE_ARGS(n)); \
      } \
      \
      template<BOOST_ASIO_VARIADIC_TPARAMS(n)> \
      void complete(BOOST_ASIO_VARIADIC_MOVE_PARAMS(n)) \
      { \
        this->work_.reset(); \
        this->handler_(BOOST_ASIO_VARIADIC_MOVE_ARGS(n)); \
      } \
      /**/
      BOOST_ASIO_VARIADIC_GENERATE(BOOST_ASIO_PRIVATE_COMPOSED_OP_DEF)
  #undef BOOST_ASIO_PRIVATE_COMPOSED_OP_DEF
  
  #endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
  
    //private:
      Impl impl_;
      Work work_;
      Handler handler_;
      unsigned invocations_;
    };
  
    template <typename Impl, typename Work, typename Handler, typename Signature>
    inline void* asio_handler_allocate(std::size_t size,
        composed_op<Impl, Work, Handler, Signature>* this_handler)
    {
      return boost_asio_handler_alloc_helpers::allocate(
          size, this_handler->handler_);
    }
  
    template <typename Impl, typename Work, typename Handler, typename Signature>
    inline void asio_handler_deallocate(void* pointer, std::size_t size,
        composed_op<Impl, Work, Handler, Signature>* this_handler)
    {
      boost_asio_handler_alloc_helpers::deallocate(
          pointer, size, this_handler->handler_);
    }
  
    template <typename Impl, typename Work, typename Handler, typename Signature>
    inline bool asio_handler_is_continuation(
        composed_op<Impl, Work, Handler, Signature>* this_handler)
    {
      return this_handler->invocations_ > 1 ? true
        : boost_asio_handler_cont_helpers::is_continuation(
            this_handler->handler_);
    }
  
    template <typename Function, typename Impl,
        typename Work, typename Handler, typename Signature>
    inline void asio_handler_invoke(Function& function,
        composed_op<Impl, Work, Handler, Signature>* this_handler)
    {
      boost_asio_handler_invoke_helpers::invoke(
          function, this_handler->handler_);
    }
  
    template <typename Function, typename Impl,
        typename Work, typename Handler, typename Signature>
    inline void asio_handler_invoke(const Function& function,
        composed_op<Impl, Work, Handler, Signature>* this_handler)
    {
      boost_asio_handler_invoke_helpers::invoke(
          function, this_handler->handler_);
    }
  
    template <typename Signature, typename Executors>
    class initiate_composed_op
    {
    public:
      typedef typename composed_io_executors<Executors>::head_type executor_type;
  
      template <typename T>
      explicit initiate_composed_op(BOOST_ASIO_MOVE_ARG(T) executors)
        : executors_(BOOST_ASIO_MOVE_CAST(T)(executors))
      {
      }
  
      executor_type get_executor() const BOOST_ASIO_NOEXCEPT
      {
        return executors_.head_;
      }
  
      template <typename Handler, typename Impl>
      void operator()(BOOST_ASIO_MOVE_ARG(Handler) handler,
          BOOST_ASIO_MOVE_ARG(Impl) impl) const
      {
        composed_op<typename decay<Impl>::type, composed_work<Executors>,
          typename decay<Handler>::type, Signature>(
            BOOST_ASIO_MOVE_CAST(Impl)(impl),
            composed_work<Executors>(executors_),
            BOOST_ASIO_MOVE_CAST(Handler)(handler))();
      }
  
    private:
      composed_io_executors<Executors> executors_;
    };
  
    template <typename Signature, typename Executors>
    inline initiate_composed_op<Signature, Executors> make_initiate_composed_op(
        BOOST_ASIO_MOVE_ARG(composed_io_executors<Executors>) executors)
    {
      return initiate_composed_op<Signature, Executors>(
          BOOST_ASIO_MOVE_CAST(composed_io_executors<Executors>)(executors));
    }
  
    template <typename IoObject>
    inline typename IoObject::executor_type
    get_composed_io_executor(IoObject& io_object)
    {
      return io_object.get_executor();
    }
  
    template <typename Executor>
    inline const Executor& get_composed_io_executor(const Executor& ex,
        typename enable_if<is_executor<Executor>::value>::type* = 0)
    {
      return ex;
    }
  } // namespace detail
  
  #if !defined(GENERATING_DOCUMENTATION)
  #if defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
  
  template <typename CompletionToken, typename Signature,
      typename Implementation, typename... IoObjectsOrExecutors>
  BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken, Signature)
  async_compose(BOOST_ASIO_MOVE_ARG(Implementation) implementation,
      BOOST_ASIO_NONDEDUCED_MOVE_ARG(CompletionToken) token,
      BOOST_ASIO_MOVE_ARG(IoObjectsOrExecutors)... io_objects_or_executors)
  {
    return async_initiate<CompletionToken, Signature>(
        detail::make_initiate_composed_op<Signature>(
          detail::make_composed_io_executors(
            detail::get_composed_io_executor(
              BOOST_ASIO_MOVE_CAST(IoObjectsOrExecutors)(
                io_objects_or_executors))...)),
        token, BOOST_ASIO_MOVE_CAST(Implementation)(implementation));
  }
  
  #else // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
  
  template <typename CompletionToken, typename Signature, typename Implementation>
  BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken, Signature)
  async_compose(BOOST_ASIO_MOVE_ARG(Implementation) implementation,
      BOOST_ASIO_NONDEDUCED_MOVE_ARG(CompletionToken) token)
  {
    return async_initiate<CompletionToken, Signature>(
        detail::make_initiate_composed_op<Signature>(
          detail::make_composed_io_executors()),
        token, BOOST_ASIO_MOVE_CAST(Implementation)(implementation));
  }
  
  # define BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR(n) \
    BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_##n
  
  # define BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_1 \
    detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T1)(x1))
  # define BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_2 \
    detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T1)(x1)), \
    detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T2)(x2))
  # define BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_3 \
    detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T1)(x1)), \
    detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T2)(x2)), \
    detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T3)(x3))
  # define BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_4 \
    detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T1)(x1)), \
    detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T2)(x2)), \
    detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T3)(x3)), \
    detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T4)(x4))
  # define BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_5 \
    detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T1)(x1)), \
    detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T2)(x2)), \
    detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T3)(x3)), \
    detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T4)(x4)), \
    detail::get_composed_io_executor(BOOST_ASIO_MOVE_CAST(T5)(x5))
  
  #define BOOST_ASIO_PRIVATE_ASYNC_COMPOSE_DEF(n) \
    template <typename CompletionToken, typename Signature, \
        typename Implementation, BOOST_ASIO_VARIADIC_TPARAMS(n)> \
    BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken, Signature) \
    async_compose(BOOST_ASIO_MOVE_ARG(Implementation) implementation, \
        BOOST_ASIO_NONDEDUCED_MOVE_ARG(CompletionToken) token, \
        BOOST_ASIO_VARIADIC_MOVE_PARAMS(n)) \
    { \
      return async_initiate<CompletionToken, Signature>( \
          detail::make_initiate_composed_op<Signature>( \
            detail::make_composed_io_executors( \
              BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR(n))), \
          token, BOOST_ASIO_MOVE_CAST(Implementation)(implementation)); \
    } \
    /**/
    BOOST_ASIO_VARIADIC_GENERATE(BOOST_ASIO_PRIVATE_ASYNC_COMPOSE_DEF)
  #undef BOOST_ASIO_PRIVATE_ASYNC_COMPOSE_DEF
  
  #undef BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR
  #undef BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_1
  #undef BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_2
  #undef BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_3
  #undef BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_4
  #undef BOOST_ASIO_PRIVATE_GET_COMPOSED_IO_EXECUTOR_5
  
  #endif // defined(BOOST_ASIO_HAS_VARIADIC_TEMPLATES)
  #endif // !defined(GENERATING_DOCUMENTATION)
  
  } // namespace asio
  } // namespace boost
  
  #include <boost/asio/detail/pop_options.hpp>
  
  #endif // BOOST_ASIO_IMPL_COMPOSE_HPP
  