text: //
  // impl/write_at.hpp
  // ~~~~~~~~~~~~~~~~~
  //
  // Copyright (c) 2003-2015 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 ASIO_IMPL_WRITE_AT_HPP
  #define ASIO_IMPL_WRITE_AT_HPP
  
  #if defined(_MSC_VER) && (_MSC_VER >= 1200)
  # pragma once
  #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
  
  #include "asio/associated_allocator.hpp"
  #include "asio/associated_executor.hpp"
  #include "asio/buffer.hpp"
  #include "asio/completion_condition.hpp"
  #include "asio/detail/array_fwd.hpp"
  #include "asio/detail/base_from_completion_cond.hpp"
  #include "asio/detail/bind_handler.hpp"
  #include "asio/detail/consuming_buffers.hpp"
  #include "asio/detail/dependent_type.hpp"
  #include "asio/detail/handler_alloc_helpers.hpp"
  #include "asio/detail/handler_cont_helpers.hpp"
  #include "asio/detail/handler_invoke_helpers.hpp"
  #include "asio/detail/handler_type_requirements.hpp"
  #include "asio/detail/throw_error.hpp"
  
  #include "asio/detail/push_options.hpp"
  
  namespace asio {
  
  template <typename SyncRandomAccessWriteDevice, typename ConstBufferSequence,
      typename CompletionCondition>
  std::size_t write_at(SyncRandomAccessWriteDevice& d,
      uint64_t offset, const ConstBufferSequence& buffers,
      CompletionCondition completion_condition, asio::error_code& ec)
  {
    ec = asio::error_code();
    asio::detail::consuming_buffers<
      const_buffer, ConstBufferSequence> tmp(buffers);
    std::size_t total_transferred = 0;
    tmp.prepare(detail::adapt_completion_condition_result(
          completion_condition(ec, total_transferred)));
    while (tmp.begin() != tmp.end())
    {
      std::size_t bytes_transferred = d.write_some_at(
          offset + total_transferred, tmp, ec);
      tmp.consume(bytes_transferred);
      total_transferred += bytes_transferred;
      tmp.prepare(detail::adapt_completion_condition_result(
            completion_condition(ec, total_transferred)));
    }
    return total_transferred;
  }
  
  template <typename SyncRandomAccessWriteDevice, typename ConstBufferSequence>
  inline std::size_t write_at(SyncRandomAccessWriteDevice& d,
      uint64_t offset, const ConstBufferSequence& buffers)
  {
    asio::error_code ec;
    std::size_t bytes_transferred = write_at(
        d, offset, buffers, transfer_all(), ec);
    asio::detail::throw_error(ec, "write_at");
    return bytes_transferred;
  }
  
  template <typename SyncRandomAccessWriteDevice, typename ConstBufferSequence>
  inline std::size_t write_at(SyncRandomAccessWriteDevice& d,
      uint64_t offset, const ConstBufferSequence& buffers,
      asio::error_code& ec)
  {
    return write_at(d, offset, buffers, transfer_all(), ec);
  }
  
  template <typename SyncRandomAccessWriteDevice, typename ConstBufferSequence,
      typename CompletionCondition>
  inline std::size_t write_at(SyncRandomAccessWriteDevice& d,
      uint64_t offset, const ConstBufferSequence& buffers,
      CompletionCondition completion_condition)
  {
    asio::error_code ec;
    std::size_t bytes_transferred = write_at(
        d, offset, buffers, completion_condition, ec);
    asio::detail::throw_error(ec, "write_at");
    return bytes_transferred;
  }
  
  #if !defined(ASIO_NO_IOSTREAM)
  
  template <typename SyncRandomAccessWriteDevice, typename Allocator,
      typename CompletionCondition>
  std::size_t write_at(SyncRandomAccessWriteDevice& d,
      uint64_t offset, asio::basic_streambuf<Allocator>& b,
      CompletionCondition completion_condition, asio::error_code& ec)
  {
    std::size_t bytes_transferred = write_at(
        d, offset, b.data(), completion_condition, ec);
    b.consume(bytes_transferred);
    return bytes_transferred;
  }
  
  template <typename SyncRandomAccessWriteDevice, typename Allocator>
  inline std::size_t write_at(SyncRandomAccessWriteDevice& d,
      uint64_t offset, asio::basic_streambuf<Allocator>& b)
  {
    asio::error_code ec;
    std::size_t bytes_transferred = write_at(d, offset, b, transfer_all(), ec);
    asio::detail::throw_error(ec, "write_at");
    return bytes_transferred;
  }
  
  template <typename SyncRandomAccessWriteDevice, typename Allocator>
  inline std::size_t write_at(SyncRandomAccessWriteDevice& d,
      uint64_t offset, asio::basic_streambuf<Allocator>& b,
      asio::error_code& ec)
  {
    return write_at(d, offset, b, transfer_all(), ec);
  }
  
  template <typename SyncRandomAccessWriteDevice, typename Allocator,
      typename CompletionCondition>
  inline std::size_t write_at(SyncRandomAccessWriteDevice& d,
      uint64_t offset, asio::basic_streambuf<Allocator>& b,
      CompletionCondition completion_condition)
  {
    asio::error_code ec;
    std::size_t bytes_transferred = write_at(
        d, offset, b, completion_condition, ec);
    asio::detail::throw_error(ec, "write_at");
    return bytes_transferred;
  }
  
  #endif // !defined(ASIO_NO_IOSTREAM)
  
  namespace detail
  {
    template <typename AsyncRandomAccessWriteDevice, typename ConstBufferSequence,
        typename CompletionCondition, typename WriteHandler>
    class write_at_op
      : detail::base_from_completion_cond<CompletionCondition>
    {
    public:
      write_at_op(AsyncRandomAccessWriteDevice& device,
          uint64_t offset, const ConstBufferSequence& buffers,
          CompletionCondition completion_condition, WriteHandler& handler)
        : detail::base_from_completion_cond<
            CompletionCondition>(completion_condition),
          device_(device),
          offset_(offset),
          buffers_(buffers),
          start_(0),
          total_transferred_(0),
          handler_(ASIO_MOVE_CAST(WriteHandler)(handler))
      {
      }
  
  #if defined(ASIO_HAS_MOVE)
      write_at_op(const write_at_op& other)
        : detail::base_from_completion_cond<CompletionCondition>(other),
          device_(other.device_),
          offset_(other.offset_),
          buffers_(other.buffers_),
          start_(other.start_),
          total_transferred_(other.total_transferred_),
          handler_(other.handler_)
      {
      }
  
      write_at_op(write_at_op&& other)
        : detail::base_from_completion_cond<CompletionCondition>(other),
          device_(other.device_),
          offset_(other.offset_),
          buffers_(other.buffers_),
          start_(other.start_),
          total_transferred_(other.total_transferred_),
          handler_(ASIO_MOVE_CAST(WriteHandler)(other.handler_))
      {
      }
  #endif // defined(ASIO_HAS_MOVE)
  
      void operator()(const asio::error_code& ec,
          std::size_t bytes_transferred, int start = 0)
      {
        switch (start_ = start)
        {
          case 1:
          buffers_.prepare(this->check_for_completion(ec, total_transferred_));
          for (;;)
          {
            device_.async_write_some_at(
                offset_ + total_transferred_, buffers_,
                ASIO_MOVE_CAST(write_at_op)(*this));
            return; default:
            total_transferred_ += bytes_transferred;
            buffers_.consume(bytes_transferred);
            buffers_.prepare(this->check_for_completion(ec, total_transferred_));
            if ((!ec && bytes_transferred == 0)
                || buffers_.begin() == buffers_.end())
              break;
          }
  
          handler_(ec, static_cast<const std::size_t&>(total_transferred_));
        }
      }
  
    //private:
      AsyncRandomAccessWriteDevice& device_;
      uint64_t offset_;
      asio::detail::consuming_buffers<
        const_buffer, ConstBufferSequence> buffers_;
      int start_;
      std::size_t total_transferred_;
      WriteHandler handler_;
    };
  
    template <typename AsyncRandomAccessWriteDevice,
        typename CompletionCondition, typename WriteHandler>
    class write_at_op<AsyncRandomAccessWriteDevice,
        asio::mutable_buffers_1, CompletionCondition, WriteHandler>
      : detail::base_from_completion_cond<CompletionCondition>
    {
    public:
      write_at_op(AsyncRandomAccessWriteDevice& device,
          uint64_t offset, const asio::mutable_buffers_1& buffers,
          CompletionCondition completion_condition,
          WriteHandler& handler)
        : detail::base_from_completion_cond<
            CompletionCondition>(completion_condition),
          device_(device),
          offset_(offset),
          buffer_(buffers),
          start_(0),
          total_transferred_(0),
          handler_(ASIO_MOVE_CAST(WriteHandler)(handler))
      {
      }
  
  #if defined(ASIO_HAS_MOVE)
      write_at_op(const write_at_op& other)
        : detail::base_from_completion_cond<CompletionCondition>(other),
          device_(other.device_),
          offset_(other.offset_),
          buffer_(other.buffer_),
          start_(other.start_),
          total_transferred_(other.total_transferred_),
          handler_(other.handler_)
      {
      }
  
      write_at_op(write_at_op&& other)
        : detail::base_from_completion_cond<CompletionCondition>(other),
          device_(other.device_),
          offset_(other.offset_),
          buffer_(other.buffer_),
          start_(other.start_),
          total_transferred_(other.total_transferred_),
          handler_(ASIO_MOVE_CAST(WriteHandler)(other.handler_))
      {
      }
  #endif // defined(ASIO_HAS_MOVE)
  
      void operator()(const asio::error_code& ec,
          std::size_t bytes_transferred, int start = 0)
      {
        std::size_t n = 0;
        switch (start_ = start)
        {
          case 1:
          n = this->check_for_completion(ec, total_transferred_);
          for (;;)
          {
            device_.async_write_some_at(offset_ + total_transferred_,
                asio::buffer(buffer_ + total_transferred_, n),
                ASIO_MOVE_CAST(write_at_op)(*this));
            return; default:
            total_transferred_ += bytes_transferred;
            if ((!ec && bytes_transferred == 0)
                || (n = this->check_for_completion(ec, total_transferred_)) == 0
                || total_transferred_ == buffer_.size())
              break;
          }
  
          handler_(ec, static_cast<const std::size_t&>(total_transferred_));
        }
      }
  
    //private:
      AsyncRandomAccessWriteDevice& device_;
      uint64_t offset_;
      asio::mutable_buffer buffer_;
      int start_;
      std::size_t total_transferred_;
      WriteHandler handler_;
    };
  
    template <typename AsyncRandomAccessWriteDevice,
        typename CompletionCondition, typename WriteHandler>
    class write_at_op<AsyncRandomAccessWriteDevice, asio::const_buffers_1,
        CompletionCondition, WriteHandler>
      : detail::base_from_completion_cond<CompletionCondition>
    {
    public:
      write_at_op(AsyncRandomAccessWriteDevice& device,
          uint64_t offset, const asio::const_buffers_1& buffers,
          CompletionCondition completion_condition,
          WriteHandler& handler)
        : detail::base_from_completion_cond<
            CompletionCondition>(completion_condition),
          device_(device),
          offset_(offset),
          buffer_(buffers),
          start_(0),
          total_transferred_(0),
          handler_(ASIO_MOVE_CAST(WriteHandler)(handler))
      {
      }
  
  #if defined(ASIO_HAS_MOVE)
      write_at_op(const write_at_op& other)
        : detail::base_from_completion_cond<CompletionCondition>(other),
          device_(other.device_),
          offset_(other.offset_),
          buffer_(other.buffer_),
          start_(other.start_),
          total_transferred_(other.total_transferred_),
          handler_(other.handler_)
      {
      }
  
      write_at_op(write_at_op&& other)
        : detail::base_from_completion_cond<CompletionCondition>(other),
          device_(other.device_),
          offset_(other.offset_),
          buffer_(other.buffer_),
          start_(other.start_),
          total_transferred_(other.total_transferred_),
          handler_(ASIO_MOVE_CAST(WriteHandler)(other.handler_))
      {
      }
  #endif // defined(ASIO_HAS_MOVE)
  
      void operator()(const asio::error_code& ec,
          std::size_t bytes_transferred, int start = 0)
      {
        std::size_t n = 0;
        switch (start_ = start)
        {
          case 1:
          n = this->check_for_completion(ec, total_transferred_);
          for (;;)
          {
            device_.async_write_some_at(offset_ + total_transferred_,
                asio::buffer(buffer_ + total_transferred_, n),
                ASIO_MOVE_CAST(write_at_op)(*this));
            return; default:
            total_transferred_ += bytes_transferred;
            if ((!ec && bytes_transferred == 0)
                || (n = this->check_for_completion(ec, total_transferred_)) == 0
                || total_transferred_ == buffer_.size())
              break;
          }
  
          handler_(ec, static_cast<const std::size_t&>(total_transferred_));
        }
      }
  
    //private:
      AsyncRandomAccessWriteDevice& device_;
      uint64_t offset_;
      asio::const_buffer buffer_;
      int start_;
      std::size_t total_transferred_;
      WriteHandler handler_;
    };
  
    template <typename AsyncRandomAccessWriteDevice, typename Elem,
        typename CompletionCondition, typename WriteHandler>
    class write_at_op<AsyncRandomAccessWriteDevice, boost::array<Elem, 2>,
        CompletionCondition, WriteHandler>
      : detail::base_from_completion_cond<CompletionCondition>
    {
    public:
      write_at_op(AsyncRandomAccessWriteDevice& device,
          uint64_t offset, const boost::array<Elem, 2>& buffers,
          CompletionCondition completion_condition, WriteHandler& handler)
        : detail::base_from_completion_cond<
            CompletionCondition>(completion_condition),
          device_(device),
          offset_(offset),
          buffers_(buffers),
          start_(0),
          total_transferred_(0),
          handler_(ASIO_MOVE_CAST(WriteHandler)(handler))
      {
      }
  
  #if defined(ASIO_HAS_MOVE)
      write_at_op(const write_at_op& other)
        : detail::base_from_completion_cond<CompletionCondition>(other),
          device_(other.device_),
          offset_(other.offset_),
          buffers_(other.buffers_),
          start_(other.start_),
          total_transferred_(other.total_transferred_),
          handler_(other.handler_)
      {
      }
  
      write_at_op(write_at_op&& other)
        : detail::base_from_completion_cond<CompletionCondition>(other),
          device_(other.device_),
          offset_(other.offset_),
          buffers_(other.buffers_),
          start_(other.start_),
          total_transferred_(other.total_transferred_),
          handler_(ASIO_MOVE_CAST(WriteHandler)(other.handler_))
      {
      }
  #endif // defined(ASIO_HAS_MOVE)
  
      void operator()(const asio::error_code& ec,
          std::size_t bytes_transferred, int start = 0)
      {
        typename asio::detail::dependent_type<Elem,
            boost::array<asio::const_buffer, 2> >::type bufs = {{
          asio::const_buffer(buffers_[0]),
          asio::const_buffer(buffers_[1]) }};
        std::size_t buffer_size0 = bufs[0].size();
        std::size_t buffer_size1 = bufs[1].size();
        std::size_t n = 0;
        switch (start_ = start)
        {
          case 1:
          n = this->check_for_completion(ec, total_transferred_);
          for (;;)
          {
            bufs[0] = asio::buffer(bufs[0] + total_transferred_, n);
            bufs[1] = asio::buffer(
                bufs[1] + (total_transferred_ < buffer_size0
                  ? 0 : total_transferred_ - buffer_size0),
                n - bufs[0].size());
            device_.async_write_some_at(offset_ + total_transferred_,
                bufs, ASIO_MOVE_CAST(write_at_op)(*this));
            return; default:
            total_transferred_ += bytes_transferred;
            if ((!ec && bytes_transferred == 0)
                || (n = this->check_for_completion(ec, total_transferred_)) == 0
                || total_transferred_ == buffer_size0 + buffer_size1)
              break;
          }
  
          handler_(ec, static_cast<const std::size_t&>(total_transferred_));
        }
      }
  
    //private:
      AsyncRandomAccessWriteDevice& device_;
      uint64_t offset_;
      boost::array<Elem, 2> buffers_;
      int start_;
      std::size_t total_transferred_;
      WriteHandler handler_;
    };
  
  #if defined(ASIO_HAS_STD_ARRAY)
  
    template <typename AsyncRandomAccessWriteDevice, typename Elem,
        typename CompletionCondition, typename WriteHandler>
    class write_at_op<AsyncRandomAccessWriteDevice, std::array<Elem, 2>,
        CompletionCondition, WriteHandler>
      : detail::base_from_completion_cond<CompletionCondition>
    {
    public:
      write_at_op(AsyncRandomAccessWriteDevice& device,
          uint64_t offset, const std::array<Elem, 2>& buffers,
          CompletionCondition completion_condition, WriteHandler& handler)
        : detail::base_from_completion_cond<
            CompletionCondition>(completion_condition),
          device_(device),
          offset_(offset),
          buffers_(buffers),
          start_(0),
          total_transferred_(0),
          handler_(ASIO_MOVE_CAST(WriteHandler)(handler))
      {
      }
  
  #if defined(ASIO_HAS_MOVE)
      write_at_op(const write_at_op& other)
        : detail::base_from_completion_cond<CompletionCondition>(other),
          device_(other.device_),
          offset_(other.offset_),
          buffers_(other.buffers_),
          start_(other.start_),
          total_transferred_(other.total_transferred_),
          handler_(other.handler_)
      {
      }
  
      write_at_op(write_at_op&& other)
        : detail::base_from_completion_cond<CompletionCondition>(other),
          device_(other.device_),
          offset_(other.offset_),
          buffers_(other.buffers_),
          start_(other.start_),
          total_transferred_(other.total_transferred_),
          handler_(ASIO_MOVE_CAST(WriteHandler)(other.handler_))
      {
      }
  #endif // defined(ASIO_HAS_MOVE)
  
      void operator()(const asio::error_code& ec,
          std::size_t bytes_transferred, int start = 0)
      {
        typename asio::detail::dependent_type<Elem,
            std::array<asio::const_buffer, 2> >::type bufs = {{
          asio::const_buffer(buffers_[0]),
          asio::const_buffer(buffers_[1]) }};
        std::size_t buffer_size0 = bufs[0].size();
        std::size_t buffer_size1 = bufs[1].size();
        std::size_t n = 0;
        switch (start_ = start)
        {
          case 1:
          n = this->check_for_completion(ec, total_transferred_);
          for (;;)
          {
            bufs[0] = asio::buffer(bufs[0] + total_transferred_, n);
            bufs[1] = asio::buffer(
                bufs[1] + (total_transferred_ < buffer_size0
                  ? 0 : total_transferred_ - buffer_size0),
                n - bufs[0].size());
            device_.async_write_some_at(offset_ + total_transferred_,
                bufs, ASIO_MOVE_CAST(write_at_op)(*this));
            return; default:
            total_transferred_ += bytes_transferred;
            if ((!ec && bytes_transferred == 0)
                || (n = this->check_for_completion(ec, total_transferred_)) == 0
                || total_transferred_ == buffer_size0 + buffer_size1)
              break;
          }
  
          handler_(ec, static_cast<const std::size_t&>(total_transferred_));
        }
      }
  
    //private:
      AsyncRandomAccessWriteDevice& device_;
      uint64_t offset_;
      std::array<Elem, 2> buffers_;
      int start_;
      std::size_t total_transferred_;
      WriteHandler handler_;
    };
  
  #endif // defined(ASIO_HAS_STD_ARRAY)
  
    template <typename AsyncRandomAccessWriteDevice, typename ConstBufferSequence,
        typename CompletionCondition, typename WriteHandler>
    inline void* asio_handler_allocate(std::size_t size,
        write_at_op<AsyncRandomAccessWriteDevice, ConstBufferSequence,
          CompletionCondition, WriteHandler>* this_handler)
    {
      return asio_handler_alloc_helpers::allocate(
          size, this_handler->handler_);
    }
  
    template <typename AsyncRandomAccessWriteDevice, typename ConstBufferSequence,
        typename CompletionCondition, typename WriteHandler>
    inline void asio_handler_deallocate(void* pointer, std::size_t size,
        write_at_op<AsyncRandomAccessWriteDevice, ConstBufferSequence,
          CompletionCondition, WriteHandler>* this_handler)
    {
      asio_handler_alloc_helpers::deallocate(
          pointer, size, this_handler->handler_);
    }
  
    template <typename AsyncRandomAccessWriteDevice, typename ConstBufferSequence,
        typename CompletionCondition, typename WriteHandler>
    inline bool asio_handler_is_continuation(
        write_at_op<AsyncRandomAccessWriteDevice, ConstBufferSequence,
          CompletionCondition, WriteHandler>* this_handler)
    {
      return this_handler->start_ == 0 ? true
        : asio_handler_cont_helpers::is_continuation(
            this_handler->handler_);
    }
  
    template <typename Function, typename AsyncRandomAccessWriteDevice,
        typename ConstBufferSequence, typename CompletionCondition,
        typename WriteHandler>
    inline void asio_handler_invoke(Function& function,
        write_at_op<AsyncRandomAccessWriteDevice, ConstBufferSequence,
          CompletionCondition, WriteHandler>* this_handler)
    {
      asio_handler_invoke_helpers::invoke(
          function, this_handler->handler_);
    }
  
    template <typename Function, typename AsyncRandomAccessWriteDevice,
        typename ConstBufferSequence, typename CompletionCondition,
        typename WriteHandler>
    inline void asio_handler_invoke(const Function& function,
        write_at_op<AsyncRandomAccessWriteDevice, ConstBufferSequence,
          CompletionCondition, WriteHandler>* this_handler)
    {
      asio_handler_invoke_helpers::invoke(
          function, this_handler->handler_);
    }
  
    template <typename AsyncRandomAccessWriteDevice, typename ConstBufferSequence,
        typename CompletionCondition, typename WriteHandler>
    inline write_at_op<AsyncRandomAccessWriteDevice,
        ConstBufferSequence, CompletionCondition, WriteHandler>
    make_write_at_op(AsyncRandomAccessWriteDevice& d,
        uint64_t offset, const ConstBufferSequence& buffers,
        CompletionCondition completion_condition, WriteHandler handler)
    {
      return write_at_op<AsyncRandomAccessWriteDevice,
        ConstBufferSequence, CompletionCondition, WriteHandler>(
          d, offset, buffers, completion_condition, handler);
    }
  } // namespace detail
  
  #if !defined(GENERATING_DOCUMENTATION)
  
  template <typename AsyncRandomAccessWriteDevice, typename ConstBufferSequence,
      typename CompletionCondition, typename WriteHandler, typename Allocator>
  struct associated_allocator<
      detail::write_at_op<AsyncRandomAccessWriteDevice,
        ConstBufferSequence, CompletionCondition, WriteHandler>,
      Allocator>
  {
    typedef typename associated_allocator<WriteHandler, Allocator>::type type;
  
    static type get(
        const detail::write_at_op<AsyncRandomAccessWriteDevice,
          ConstBufferSequence, CompletionCondition, WriteHandler>& h,
        const Allocator& a = Allocator()) ASIO_NOEXCEPT
    {
      return associated_allocator<WriteHandler, Allocator>::get(h.handler_, a);
    }
  };
  
  template <typename AsyncRandomAccessWriteDevice, typename ConstBufferSequence,
      typename CompletionCondition, typename WriteHandler, typename Executor>
  struct associated_executor<
      detail::write_at_op<AsyncRandomAccessWriteDevice,
        ConstBufferSequence, CompletionCondition, WriteHandler>,
      Executor>
  {
    typedef typename associated_executor<WriteHandler, Executor>::type type;
  
    static type get(
        const detail::write_at_op<AsyncRandomAccessWriteDevice,
          ConstBufferSequence, CompletionCondition, WriteHandler>& h,
        const Executor& ex = Executor()) ASIO_NOEXCEPT
    {
      return associated_executor<WriteHandler, Executor>::get(h.handler_, ex);
    }
  };
  
  #endif // !defined(GENERATING_DOCUMENTATION)
  
  template <typename AsyncRandomAccessWriteDevice, typename ConstBufferSequence,
      typename CompletionCondition, typename WriteHandler>
  inline ASIO_INITFN_RESULT_TYPE(WriteHandler,
      void (asio::error_code, std::size_t))
  async_write_at(AsyncRandomAccessWriteDevice& d,
      uint64_t offset, const ConstBufferSequence& buffers,
      CompletionCondition completion_condition,
      ASIO_MOVE_ARG(WriteHandler) handler)
  {
    // If you get an error on the following line it means that your handler does
    // not meet the documented type requirements for a WriteHandler.
    ASIO_WRITE_HANDLER_CHECK(WriteHandler, handler) type_check;
  
    async_completion<WriteHandler,
      void (asio::error_code, std::size_t)> init(handler);
  
    detail::write_at_op<AsyncRandomAccessWriteDevice, ConstBufferSequence,
      CompletionCondition, ASIO_HANDLER_TYPE(
        WriteHandler, void (asio::error_code, std::size_t))>(
          d, offset, buffers, completion_condition, init.handler)(
            asio::error_code(), 0, 1);
  
    return init.result.get();
  }
  
  template <typename AsyncRandomAccessWriteDevice, typename ConstBufferSequence,
      typename WriteHandler>
  inline ASIO_INITFN_RESULT_TYPE(WriteHandler,
      void (asio::error_code, std::size_t))
  async_write_at(AsyncRandomAccessWriteDevice& d,
      uint64_t offset, const ConstBufferSequence& buffers,
      ASIO_MOVE_ARG(WriteHandler) handler)
  {
    // If you get an error on the following line it means that your handler does
    // not meet the documented type requirements for a WriteHandler.
    ASIO_WRITE_HANDLER_CHECK(WriteHandler, handler) type_check;
  
    async_completion<WriteHandler,
      void (asio::error_code, std::size_t)> init(handler);
  
    detail::write_at_op<AsyncRandomAccessWriteDevice, ConstBufferSequence,
      detail::transfer_all_t, ASIO_HANDLER_TYPE(
        WriteHandler, void (asio::error_code, std::size_t))>(
          d, offset, buffers, transfer_all(), init.handler)(
            asio::error_code(), 0, 1);
  
    return init.result.get();
  }
  
  #if !defined(ASIO_NO_IOSTREAM)
  
  namespace detail
  {
    template <typename Allocator, typename WriteHandler>
    class write_at_streambuf_op
    {
    public:
      write_at_streambuf_op(
          asio::basic_streambuf<Allocator>& streambuf,
          WriteHandler& handler)
        : streambuf_(streambuf),
          handler_(ASIO_MOVE_CAST(WriteHandler)(handler))
      {
      }
  
  #if defined(ASIO_HAS_MOVE)
      write_at_streambuf_op(const write_at_streambuf_op& other)
        : streambuf_(other.streambuf_),
          handler_(other.handler_)
      {
      }
  
      write_at_streambuf_op(write_at_streambuf_op&& other)
        : streambuf_(other.streambuf_),
          handler_(ASIO_MOVE_CAST(WriteHandler)(other.handler_))
      {
      }
  #endif // defined(ASIO_HAS_MOVE)
  
      void operator()(const asio::error_code& ec,
          const std::size_t bytes_transferred)
      {
        streambuf_.consume(bytes_transferred);
        handler_(ec, bytes_transferred);
      }
  
    //private:
      asio::basic_streambuf<Allocator>& streambuf_;
      WriteHandler handler_;
    };
  
    template <typename Allocator, typename WriteHandler>
    inline void* asio_handler_allocate(std::size_t size,
        write_at_streambuf_op<Allocator, WriteHandler>* this_handler)
    {
      return asio_handler_alloc_helpers::allocate(
          size, this_handler->handler_);
    }
  
    template <typename Allocator, typename WriteHandler>
    inline void asio_handler_deallocate(void* pointer, std::size_t size,
        write_at_streambuf_op<Allocator, WriteHandler>* this_handler)
    {
      asio_handler_alloc_helpers::deallocate(
          pointer, size, this_handler->handler_);
    }
  
    template <typename Allocator, typename WriteHandler>
    inline bool asio_handler_is_continuation(
        write_at_streambuf_op<Allocator, WriteHandler>* this_handler)
    {
      return asio_handler_cont_helpers::is_continuation(
          this_handler->handler_);
    }
  
    template <typename Function, typename Allocator, typename WriteHandler>
    inline void asio_handler_invoke(Function& function,
        write_at_streambuf_op<Allocator, WriteHandler>* this_handler)
    {
      asio_handler_invoke_helpers::invoke(
          function, this_handler->handler_);
    }
  
    template <typename Function, typename Allocator, typename WriteHandler>
    inline void asio_handler_invoke(const Function& function,
        write_at_streambuf_op<Allocator, WriteHandler>* this_handler)
    {
      asio_handler_invoke_helpers::invoke(
          function, this_handler->handler_);
    }
  
    template <typename Allocator, typename WriteHandler>
    inline write_at_streambuf_op<Allocator, WriteHandler>
    make_write_at_streambuf_op(
        asio::basic_streambuf<Allocator>& b, WriteHandler handler)
    {
      return write_at_streambuf_op<Allocator, WriteHandler>(b, handler);
    }
  } // namespace detail
  
  #if !defined(GENERATING_DOCUMENTATION)
  
  template <typename Allocator, typename WriteHandler, typename Allocator1>
  struct associated_allocator<
      detail::write_at_streambuf_op<Allocator, WriteHandler>,
      Allocator1>
  {
    typedef typename associated_allocator<WriteHandler, Allocator1>::type type;
  
    static type get(
        const detail::write_at_streambuf_op<Allocator, WriteHandler>& h,
        const Allocator1& a = Allocator1()) ASIO_NOEXCEPT
    {
      return associated_allocator<WriteHandler, Allocator1>::get(h.handler_, a);
    }
  };
  
  template <typename Executor, typename WriteHandler, typename Executor1>
  struct associated_executor<
      detail::write_at_streambuf_op<Executor, WriteHandler>,
      Executor1>
  {
    typedef typename associated_executor<WriteHandler, Executor1>::type type;
  
    static type get(
        const detail::write_at_streambuf_op<Executor, WriteHandler>& h,
        const Executor1& ex = Executor1()) ASIO_NOEXCEPT
    {
      return associated_executor<WriteHandler, Executor1>::get(h.handler_, ex);
    }
  };
  
  #endif // !defined(GENERATING_DOCUMENTATION)
  
  template <typename AsyncRandomAccessWriteDevice, typename Allocator,
      typename CompletionCondition, typename WriteHandler>
  inline ASIO_INITFN_RESULT_TYPE(WriteHandler,
      void (asio::error_code, std::size_t))
  async_write_at(AsyncRandomAccessWriteDevice& d,
      uint64_t offset, asio::basic_streambuf<Allocator>& b,
      CompletionCondition completion_condition,
      ASIO_MOVE_ARG(WriteHandler) handler)
  {
    // If you get an error on the following line it means that your handler does
    // not meet the documented type requirements for a WriteHandler.
    ASIO_WRITE_HANDLER_CHECK(WriteHandler, handler) type_check;
  
    async_completion<WriteHandler,
      void (asio::error_code, std::size_t)> init(handler);
  
    async_write_at(d, offset, b.data(), completion_condition,
      detail::write_at_streambuf_op<Allocator, ASIO_HANDLER_TYPE(
        WriteHandler, void (asio::error_code, std::size_t))>(
          b, init.handler));
  
    return init.result.get();
  }
  
  template <typename AsyncRandomAccessWriteDevice, typename Allocator,
      typename WriteHandler>
  inline ASIO_INITFN_RESULT_TYPE(WriteHandler,
      void (asio::error_code, std::size_t))
  async_write_at(AsyncRandomAccessWriteDevice& d,
      uint64_t offset, asio::basic_streambuf<Allocator>& b,
      ASIO_MOVE_ARG(WriteHandler) handler)
  {
    // If you get an error on the following line it means that your handler does
    // not meet the documented type requirements for a WriteHandler.
    ASIO_WRITE_HANDLER_CHECK(WriteHandler, handler) type_check;
  
    async_completion<WriteHandler,
      void (asio::error_code, std::size_t)> init(handler);
  
    async_write_at(d, offset, b.data(), transfer_all(),
      detail::write_at_streambuf_op<Allocator, ASIO_HANDLER_TYPE(
        WriteHandler, void (asio::error_code, std::size_t))>(
          b, init.handler));
  
    return init.result.get();
  }
  
  #endif // !defined(ASIO_NO_IOSTREAM)
  
  } // namespace asio
  
  #include "asio/detail/pop_options.hpp"
  
  #endif // ASIO_IMPL_WRITE_AT_HPP
  