On Mon, Jul 19, 2010 at 6:42 PM, Daniel Walker <daniel.j.walker@gmail.com>wrote:
On Mon, Jul 19, 2010 at 5:37 PM, David Sankel <camior@gmail.com> wrote:
I'm wondering if there's a way I can generically get the result type of boost bind.
I'd like to write something along these lines:
template< typename StreamT, typename Sink > typename boost::result_of< boost::Bind( StreamT, boost::arg<1>, Sink )
::type apSink( StreamT t, Sink sk ) { return boost::bind( t , _1 , sk ); }
I'm not interested in a boost::function solution because I require that uses apSink's result can be inlined. Any ideas? Perhaps one of these other bind-like libraries has an answer to this.
To my knowledge there is no general way to declare the return type of boost::bind (or a Boost Lambda expression). In C++03 the best we can do is boost::function, which can store arbitrary function objects without having to know the type.
Thanks Daniel. I have found a way do, somewhat awkwardly, what I want in C++03 so I'll give my solution below. Look at the header bind.hpp in the section commented "generic function objects", the return types are shown to be of the form: _bi::bind_t< R , F , typename _bi::list_av_1<A1>::type > Where R is either the Z in a bind<Z> form or _bi::unspecified for the more common form. The list of arguments are part of the third template parameter. So my function then becomes: template< typename StreamT, typename Sink > boost::_bi::bind_t< boost::_bi::unspecified , StreamT , typename boost::_bi::list_av_2< Sink , boost::arg<1> >::type > apSink( StreamT t, Sink sk ) { return boost::bind( t , sk , _1 ); } However, this is really bad form as is anytime when passing an instance of bind_t to an outside function. The reason is that bind_t doesn't have normal callable semantics if it is used within another call to bind. To fix this problem boost::protect must be used. The following is the final version of my function: template< typename StreamT, typename Sink > boost::_bi::protected_bind_t< boost::_bi::bind_t< boost::_bi::unspecified , StreamT , typename boost::_bi::list_av_2< Sink , boost::arg<1> >::type > > apSink( StreamT t, Sink sk ) { return boost::protect( boost::bind( t , sk , _1 ) ); } Works great! David -- David Sankel Sankel Software www.sankelsoftware.com 585 617 4748 (Office)