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

From: David Abrahams (dave_at_[hidden])
Date: 2006-04-27 13:27:01

Frank Birbacher <bloodymir.crap_at_[hidden]> 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 <boost/iterator/transform_iterator.hpp>
> #include <boost/lambda/lambda.hpp>
>
> 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::lambda::lambda_functor_base<boost::lambda::explicit_return_type_action<int*>,
> boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::addressof_action>,
> boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::placeholder<1>
>>, 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