[Boost-users] boost::result_of and gcc

From: Martin Ecker (martin.ecker_at_[hidden])
Date: 2007-09-28 02:09:13

Hello,

I'm running into a problem when using boost::result_of with gcc 3.4.2 
and 4.2.1 (with MingW).

The following program compiles fine with Visual C++ 8.0, but not with gcc:

-------------------------------
#include <boost/utility/result_of.hpp>

struct test_function1
{
     template <typename SignatureT>
     struct result;

     template <typename T>
     struct result<test_function1 (T)>
     {
         typedef T type;
     };

     template <typename T>
     T operator () (T t) const
     {
         return t;
     }
};

template <typename ArgT>
struct test_function2
{
     template <typename SignatureT>
     struct result;

     template <typename T>
     struct result<test_function2 (T)>
     {
         typedef T type;
     };

     template <typename T>
     T operator () (T t) const
     {
         return t;
     }
};

int main(int argc, char *argv[])
{
     typedef boost::result_of<
         test_function1(int)>::type result_type;
     typedef boost::result_of<
         test_function2<float>(int)>::type result_type;
     return 0;
}
-------------------------------

The error message I get is for the second typedef using test_function2:

E:/Projects/Third Party/boost/boost/utility/result_of.hpp: In 
instantiation of 
`boost::detail::result_of_nested_result<test_function2<float>, 
test_function2<float> ()(int)>':

E:/Projects/Third Party/boost/boost/utility/result_of.hpp:75: 
instantiated from 
`boost::detail::result_of_impl<test_function2<float>, 
test_function2<float> ()(int),  false>'
E:/Projects/Third 
Party/boost/boost/utility/detail/result_of_iterate.hpp:24: 
instantiated from `boost::result_of<test_function2<float> ()(int)>'
main.cpp:43:   instantiated from here
E:/Projects/Third Party/boost/boost/utility/result_of.hpp:68: error: 
invalid use of undefined type `struct 
test_function2<float>::result<test_function2<float> ()(int)>'

I get the same error if I simply wrap test_function1 in another 
template class as nested struct and then use it instead of test_function2.

Am I attempting to do something fundamentally wrong here, or is it a 
bug in gcc?

Thanks,
Martin