CODEWITHSUNDEEP
c++visual-studio-2010visual-c++boostboost-range
JohnB
JohnB

Reputation: 13713

boost::adaptors::strided cannot be used after boost::adaptors::transformed?

The following does not compile on Visual Studio 2010:

std::vector<int> v;
for (int i = 0; i < 10; ++i) v.push_back (i);

struct TrivialTrafo {
    typedef int result_type;
    int operator () (int i) const { return 1; }
};
auto x = v | boost::adaptors::transformed (TrivialTrafo ()) 
     | boost::adaptors::strided (2);

The compiler complains (error message originally in German, my translation):

error C2664: 
'boost::range_detail::strided_iterator<BaseIterator,Category>::strided_iterator
(const boost::range_detail::strided_iterator<BaseIterator,Category> &)':
Conversion of parameter 1 from
'boost::range_detail::strided_iterator<BaseIterator,Category>' into
'const boost::range_detail::strided_iterator<BaseIterator,Category> &'
not possible 
          with
          [
BaseIterator=boost::iterators::transform_iterator<
TEST_rectnew_getRows::TrivialTrafo,std::_Vector_iterator<
std::_Vector_val<int,std::allocator<int>>>>,
Category=boost::iterators::detail::iterator_category_with_traversal<
std::input_iterator_tag,boost::iterators::random_access_traversal_tag>
          ]
          and
          [
BaseIterator=boost::iterators::transform_iterator<
TEST_rectnew_getRows::TrivialTrafo,std::_Vector_iterator<
std::_Vector_val<int,std::allocator<int>>>>,
Category=boost::iterators::random_access_traversal_tag
          ]
          and
          [              
BaseIterator=boost::iterators::transform_iterator<
TEST_rectnew_getRows::TrivialTrafo,
std::_Vector_iterator<std::_Vector_val<int,std::allocator<int>>>
>,
Category=boost::iterators::detail::iterator_category_with_traversal<
std::input_iterator_tag,boost::iterators::random_access_traversal_tag>
          ]

I'm using Boost 1.57.

Obviously operator | tries to construct a strided_range with the wrong Category template parameter value?

Is this a bug, or am I doing anything wrong?

Upvotes: 3

Views: 362

Answers (2)

ecatmur
ecatmur

Reputation: 157354

Yeah, it's a bug in Neil Groves' rewrite of strided.hpp (since 1.56, so you could revert to that version of boost if you need to). I've submitted a ticket: https://svn.boost.org/trac/boost/ticket/10989

One-line fix:

--- a/include/boost/range/adaptor/strided.hpp
+++ b/include/boost/range/adaptor/strided.hpp
@@ -603,7 +603,7 @@ namespace boost
         template<
             class Rng,
             class Category =
-                typename iterator_traversal<
+                typename iterators::pure_iterator_traversal<
                     typename range_iterator<Rng>::type
                 >::type
         >

Upvotes: 5

sehe
sehe

Reputation: 393064

I think you're confused. It actually works fine:

#include <boost/range/adaptors.hpp>
#include <iostream>

struct TrivialTrafo {
    typedef int result_type;
    int operator () (int i) const { return i; }
};

int main()
{
    std::vector<int> v;
    for (int i = 0; i < 10; ++i) v.push_back (i);

    for (auto&& x : v | boost::adaptors::transformed (TrivialTrafo ()) 
        | boost::adaptors::strided (2))
    {
        std::cout << x << " ";
    }
}

Prints

0 2 4 6 8

Looks like you expected the transformation to take an iterator instead of the range's value type?

UPDATE Ah, it might be a regression/change in the Boost Range library, since it doesn't compile Live On Coliru

This means it does work with Boost 1.55, but not with whatever Coliru uses:

http://coliru.stacked-crooked.com/a/f7a2ee559e0cf008 says that's 1.57

Upvotes: 1

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