Re: [Boost-users] [lambda] (was:[mpl]) no result_type defined

Frank Birbacher writes:

Hi!

I want to create a container of pointers to objects in a range (first,last(. I tried to use mpl, but have been without success. I understand, that the lambda "&_1" cannot specify its concrete return type, so I added ret<T>(...). But the resulting lambda is rejected by the make_transform_iterator function. I'm using boost 1.33.0 on gcc 4.0.2

I'm pretty certain this isn't an mpl problem. It looks like it's all about Boost.Lambda...

//****** CODE BEGIN ****** #include <vector> #include <iterator> #include #include

template<typename Iterator> void foo(Iterator first, Iterator last) { using boost::make_transform_iterator; using namespace boost::lambda;

typedef typename std::iterator_traits<Iterator>::pointer Pointer; std::vector<Pointer> objectPointers( make_transform_iterator(first, ret<Pointer>(&_1)), make_transform_iterator(last, ret<Pointer>(&_1)) ); // ... }

int main() { std::vector<int> v; //instantiate template: foo(v.begin(), v.end()); } //***** CODE END ******

// ** ERROR on GCC 4.0.2: ** /mnt/daten/develop/boost/boost/iterator/transform_iterator.hpp:43: Fehler: kein Typ namens »result_type« in »class boost::lambda::lambda_functor, boost::tuples::tupleboost::lambda::addressof_action, boost::tuples::tuple

...

, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type> > >, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type> > >«

-- Dave Abrahams Boost Consulting www.boost-consulting.com