Marco wrote:
On Sun, 07 Oct 2007 10:41:52 +0200, Marco Costalba <mcostalba@gmail.com> wrote:
I would think to fix completely the problem reported by Joel we could write instead:
boost::is_convertible<F, boost::function<T> >
But for unknown reasons this fails! All types of function pointers match!
Could someone please be so kind to enlight me?
Thanks Marco
Because boost::function has a constructor whose behavior is like this:
template< typename Functor > function (Functor const& f)
it skips only integral type through enable_if.
So, except integral, everything is convertible to boost::function even apples.
In order to implement signature deduction I exploits a support utility used in the implementation of boost::function and a lot of metaprogramming. Give a glance to detail::function::get_function_tag in function_base.hpp, in order to learn how to discern between different kind of functors.
Tobias (Schwinger) has this excellent library for dealing with function detection: Boost.function_types. It's in SVN now... However, I do not think this will help at all. Ok, so, say we have a polymorphic function (object) called pf. Then we have an overload set with 5 signatures, ov. pf can deal with 3 of them (say the first three). Now, how do you automatically "assign" pf to the first three overloads? You can't. There's no way to detect the signature of a template function (the operator()): Here's what I mean. Using the "add" syntax: ov.add(pf); // which one? duh! Regards, -- Joel de Guzman http://www.boost-consulting.com http://spirit.sf.net