Re: [boost] Asio, run-time polymorphism

From: Christopher Kohlhoff (chris_at_[hidden])
Date: 2006-02-26 07:50:32

Hi,

--- stas garifulin <s.garifulin_at_[hidden]> wrote:
<snip>
> In other words i'm talking about some infrastructure like
> boost::iostreams but built on top of asio dispatcher. Async
> analogue of boost::iostreams which allows me to create async
> chains of filters in run-time. For example, it can be done
> with non-templated versions of functions async_read,
> async_write, handler parameter of this functions will have
> type like boost::function<void (asio::error, size_T)>. SSL
> class could be implemented as such async filter and would
> allow attaching at run-time.

Dynamic chaining of filters is something I consider beyond the
scope of asio. Of course, it could be implemented as a library
on top of asio.

However, I am planning to add virtual wrapper stream templates
that could be used to allow runtime polymorphism with streams.
It might look something like:

template <
  typename Const_Buffers,
  typename Mutable_Buffers,
  typename Handler>
class polymorphic_stream_base
{
public:
  virtual size_t read_some(const Mutable_Buffers& bufs) = 0;
  virtual void async_read_some(const Mutable_Buffers& bufs,
      Handler handler) = 0;
  virtual size_t write_some(const Const_Buffers& bufs) = 0;
  virtual void async_write_some(const Const_Buffers& bufs,
      Handler handler) = 0;
};

template <
  typename Stream,
  typename Const_Buffers,
  typename Mutable_Buffers,
  typename Handler>
class polymorphic_stream
  : public polymorphic_stream_base<...>
{
  ...
};

This might be used to accomplish the same sort of thing as you
describe.

Cheers,
Chris