Using function_traits

From: Marshall Clow (marshall_at_[hidden])
Date: 2002-11-27 13:35:47

I'm trying to use the function traits to extract the return type of a template parameter,
but it's not compiling.

Any ideas what's wrong here?

-------- begin simplified code ------

template<typename Proc>
class CacheValue {
        typedef boost::function_traits<Proc>::R ReturnType;

        template<typename Arg1>
        ReturnType operator () ( Arg1 arg1 ) { /* do something */ }
        };

CacheValue<unsigned long (*) ( unsigned long )> aValue;

-------- end simplified code ------

Gets the error:

Error   : illegal use of incomplete struct/union/class 'boost::detail::function_traits_helper<unsigned long (**)(unsigned long)>'
 (point of instantiation: 'main()')
  (instantiating: 'CacheValue<unsigned long (*)(unsigned long)>')
   (instantiating: 'boost::function_traits<unsigned long (*)(unsigned long)>')
function_traits.hpp line 170   public detail::function_traits_helper<typename add_pointer<Function>::type>

Error   : 'R' is not a member of class 'boost::function_traits<unsigned long (*)(unsigned long)>'
 (point of instantiation: 'main()')
  (instantiating: 'CacheValue<unsigned long (*)(unsigned long)>')
HelloWorld.cp line 57   CacheValue<TickGetter> ticks ( GetCount );

Environment:
        MacOS 10.2.2, CodeWarrior 8.3, boost from CVS this morning.

It seems as if the "add_pointer" in function_traits_helper is messing things up.
Of course, it's more likely that I am using this wrong ;-)

Thanks in advance!
-- 
-- Marshall
Marshall Clow     Idio Software   <mailto:marshall_at_[hidden]>
Hey! Who messed with my anti-paranoia shot?