|  | 
        A wait handler must meet the requirements for a handler.
        A value h of a wait handler
        class should work correctly in the expression h(ec),
        where ec is an lvalue of
        type const error_code.
      
A free function as a wait handler:
void wait_handler( const asio::error_code& ec) { ... }
A wait handler function object:
struct wait_handler { ... void operator()( const asio::error_code& ec) { ... } ... };
        A non-static class member function adapted to a wait handler using bind():
      
void my_class::wait_handler( const asio::error_code& ec) { ... } ... socket.async_wait(..., boost::bind(&my_class::wait_handler, this, asio::placeholders::error));