One type traits class (or something like that) to get the return type of a pointer to function

Hi all.

I want to build a template class to extract the return type of a
pointer to function

Something like:

template<typename CB>
class ReturnTypeExtractor {
typedef ReturnType .... ??? :-(
};

....
// user code

typedef FooObject * (*CallBackType)();

typedef ReturnTypeExtractor<CallBackTypemyReturnType; //
myReturnType is FooObject *

How can I accomplish this?

Thanks In Advance

Diego
HP

re: One type traits class (or something like that) to get the return type of a pointer to function

Diego Martins wrote:
Here is some code I use:

template < typename F >
struct nullary_function_traits {

typedef typename F::result_type result_type;

};

template < typename R >
struct nullary_function_traits< R (*)( void ) {

typedef R result_type;

};


Best

Kai-Uwe Bux

re: One type traits class (or something like that) to get the return type of a pointer to function

Diego Martins wrote:#include <functional>

std::tr1::result_of<CallBackType>::type;

That is, if you have TR1. For details, see section 6.4 of my book, "The
Standard C++ Library Extensions: a Tutorial and Reference." You can get
a complete implementation of TR1 from Dinkumware, www.dinkumware.com.

result_of might also be available from boost. It was developed from a
couple of similar things there, and they've made some adaptations to
support TR1.

The problem in rolling your own is that you can't write a template that
takes an arbitrary number of arguments, so you can't easily extract the
return type unless you know how may arguments the function takes:

template <class Ty>
struct result0;

template <class Ret>
struct result0<Ret(*)()>
{
typedef Ret type;
};

template <class Ty>
struct result1;

template <class Ret, class Arg0>
struct result1<Ret(*)(Arg0)>
{
typedef Ret type;
};

and so on.

re: One type traits class (or something like that) to get the return type of a pointer to function

Pete Becker wrote:
It certainly is. That's where it came from. Most of TR1 was first
created in boost...you should know that.

re: One type traits class (or something like that) to get the return type of a pointer to function

Noah Roberts wrote:I certainly do know that much of TR1 came from Boost. That doesn't mean
that Boost provides everything that's in TR1.

As I said, result_of came from a couple of things in Boost. My
recollection is that those things were somewhat different from what
eventually turned into result_of. I haven't looked to see whether the
final version of std::tr1::result_of is available from Boost. I'm not
going to say that it is, just because it's based on things from there.

--
-- Pete

Author of "The Standard C++ Library Extensions: a Tutorial and Reference."
For more information about this book, see www.petebecker.com/tr1book.

re: One type traits class (or something like that) to get the return type of a pointer to function

Kai-Uwe Bux wrote:thank you! your solution is great for dealing with callbacks without
parameters

thanks all for the tr1 and boost hints, but I don't want to install any
addicional libraries now (due project policies and my personal taste
for making stuff manually . it is a good way to learn things)

by the way, there is a good link I've found somewhere in another thread
http://erdani.org/publications/traits.html

Cheers
Diego
HP