Re: [Boost-Users] Using function_traits

From: John Maddock (john_maddock_at_[hidden])
Date: 2002-11-29 06:45:13

> 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?

Yes, function_traits takes a function type as parameter, *not* a function
pointer type:

function_traits<int (int, double)> // OK
function_traits<int (*)(int, double)> // not OK.

So throw in a remove_pointer into your code and everything should be well:

> -------- begin simplified code ------
>
 template<typename Proc>
class CacheValue {
typedef boost::remove_pointer<Proc>::type np_type;
typedef boost::function_traits<np_type>::R ReturnType;

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

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

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

John Maddock
http://ourworld.compuserve.com/homepages/john_maddock/index.htm