[boost] [function] Get "raw" pointer to contained function/functor

From: François Duranleau (duranlef_at_[hidden])
Date: 2007-02-23 11:48:39

Hi!

I have been struggling again recently with Boost.Function and Python 
bindings, and in order to use this library transparently from the Python 
side, I need to extract the contained function/functor, but only the type 
information available is a std::type_info object (available now with the 
new target_type() member function in RC_1_34_0), so I can not simply use 
the member function target<>(). Thus, I need an extra function to get the 
"raw" pointer to the contained function/functor.

I played with the Boost.Function source code a little bit to see how it 
could be done. We only need to patch the file 
boost/function/function_base.hpp. The patched file is available here:

http://tinyurl.com/ypa8vt

I also put a patch file (a diff with the original function_base.hpp in 
RC_1_34_0) and a test file.

The idea is, of course, to expose in some way the internal functor member 
(a detail::function::function_buffer object). I chose to simply add two 
member functions:

void (*func_ptr() const)();
const void* obj_ptr() const;

The distinction is required because, as we know, pointers to function and 
regular pointers can not be cast to and from each other. func_ptr() 
returns 0 if the content is actually a functor, and similarly, obj_ptr() 
returns 0 if the content is actually a pointer to function. Thus at the 
same time, it provides a way to test if the content is a pointer to 
function or not.

Is there any interest to add this functionality to Boost.Function?

-- 
François Duranleau
LIGUM, Université de Montréal