range-v3 "ranges::to" not working with "etl::vector"

[pwhittin]

The following short sample program demonstrates the issue:

#include <iostream>
#include <vector>
#include <etl/string.h>
#include <etl/vector.h>
#include <range/v3/all.hpp>

using Name = etl::string<20>;

static constexpr auto ExpandName = [](const auto& name) { return ranges::views::repeat_n(name, 3); };

int main()
{
    {
        using Names = std::vector<Name>;
        auto names{Names{Name{"Fred"}, Name{"Sam"}, Name{"Peter"}}};
        auto expandedNames{names | ranges::views::transform(ExpandName) | ranges::views::join | ranges::to<Names>};
        for (const auto& name : expandedNames)
            std::cout << name.data() << std::endl;
    }

    {
        using Names = etl::vector<Name, 100>;
        auto names{Names{Name{"Fred"}, Name{"Sam"}, Name{"Peter"}}};

         // The following line will not compile
        auto expandedNames{names | ranges::views::transform(ExpandName) | ranges::views::join | ranges::to<Names>};

    }

    return 0;
}

Using ETL 20.35.0 and Range-v3 0.12.0, the error messages from gcc (Ubuntu 11.3.0-1ubuntu1~22.04) 11.3.0, executing gcc -Ietl/include -Irange-v3/include main.cpp are:

etl/include/etl/iterator.h:64:51: error: no type named ‘iterator_category’ in ‘struct ranges::common_iterator<ranges::basic_iterator<ranges::join_view<ranges::transform_view<ranges::ref_view<etl::vector<etl::stri
ng<20>, 100> >, <lambda(const auto:10&)> > >::cursor<false> >, ranges::default_sentinel_t>’
   64 |     typedef typename TIterator::iterator_category iterator_category;
      |                                                   ^~~~~~~~~~~~~~~~~                                                                                                                                         etl/include/etl/iterator.h:65:51: error: no type named ‘value_type’ in ‘struct ranges::common_iterator<ranges::basic_iterator<ranges::join_view<ranges::transform_view<ranges::ref_view<etl::vector<etl::string<20>,
 100> >, <lambda(const auto:10&)> > >::cursor<false> >, ranges::default_sentinel_t>’
   65 |     typedef typename TIterator::value_type        value_type;
      |                                                   ^~~~~~~~~~             
etl/include/etl/iterator.h:67:51: error: no type named ‘pointer’ in ‘struct ranges::common_iterator<ranges::basic_iterator<ranges::join_view<ranges::transform_view<ranges::ref_view<etl::vector<etl::string<20>, 10
0> >, <lambda(const auto:10&)> > >::cursor<false> >, ranges::default_sentinel_t>’
   67 |     typedef typename TIterator::pointer           pointer;     
      |                                                   ^~~~~~~    
etl/include/etl/iterator.h:68:51: error: no type named ‘reference’ in ‘struct ranges::common_iterator<ranges::basic_iterator<ranges::join_view<ranges::transform_view<ranges::ref_view<etl::vector<etl::string<20>, 
100> >, <lambda(const auto:10&)> > >::cursor<false> >, ranges::default_sentinel_t>’
   68 |     typedef typename TIterator::reference         reference;

[jwellbelove]

Could you try changing line 88 in vector.h from
typedef typename etl::iterator_traits<iterator>::difference_type difference_type;
to
typedef ptrdiff_t difference_type;

[pwhittin]

I did what you asked:

I executed g++ --std=c++20 -Irange-v3/include/ -Ietl/include/ main.cpp and got these errors:

etl/include/etl/iterator.h:64:51: error: no type named ‘iterator_category’ in ‘struct ranges::common_iterator<ranges::basic_iterator<ranges::join_view<ranges::transform_view<ranges::ref_view<etl::vector<etl::stri
ng<20>, 100> >, <lambda(const auto:28&)> > >::cursor<false> >, ranges::default_sentinel_t>’
   64 |     typedef typename TIterator::iterator_category iterator_category;
      |                                                   ^~~~~~~~~~~~~~~~~                                                                                                                                         etl/include/etl/iterator.h:65:51: error: no type named ‘value_type’ in ‘struct ranges::common_iterator<ranges::basic_iterator<ranges::join_view<ranges::transform_view<ranges::ref_view<etl::vector<etl::string<20>,
 100> >, <lambda(const auto:28&)> > >::cursor<false> >, ranges::default_sentinel_t>’
   65 |     typedef typename TIterator::value_type        value_type;
      |                                                   ^~~~~~~~~~             
etl/include/etl/iterator.h:67:51: error: no type named ‘pointer’ in ‘struct ranges::common_iterator<ranges::basic_iterator<ranges::join_view<ranges::transform_view<ranges::ref_view<etl::vector<etl::string<20>, 10
0> >, <lambda(const auto:28&)> > >::cursor<false> >, ranges::default_sentinel_t>’
   67 |     typedef typename TIterator::pointer           pointer;     
      |                                                   ^~~~~~~    
etl/include/etl/iterator.h:68:51: error: no type named ‘reference’ in ‘struct ranges::common_iterator<ranges::basic_iterator<ranges::join_view<ranges::transform_view<ranges::ref_view<etl::vector<etl::string<20>, 
100> >, <lambda(const auto:28&)> > >::cursor<false> >, ranges::default_sentinel_t>’
   68 |     typedef typename TIterator::reference         reference;

Just to be sure I executed head -n 90 etl/include/etl/vector.h | tail -n 26 in the project directory, and got:

//***************************************************************************
/// The base class for specifically sized vectors.
/// Can be used as a reference type for all vectors containing a specific type.
///\ingroup vector
//***************************************************************************
template <typename T>
class ivector : public etl::vector_base
{
  public:
    typedef T value_type;
    typedef T& reference;
    typedef const T& const_reference;
#if ETL_USING_CPP11
    typedef T&& rvalue_reference;
#endif
    typedef T* pointer;
    typedef const T* const_pointer;
    typedef T* iterator;
    typedef const T* const_iterator;
    typedef ETL_OR_STD::reverse_iterator<iterator> reverse_iterator;
    typedef ETL_OR_STD::reverse_iterator<const_iterator> const_reverse_iterator;
    typedef size_t size_type;
    typedef ptrdiff_t difference_type;
    // typedef typename etl::iterator_traits<iterator>::difference_type difference_type;

  protected:

[jwellbelove]

It looks like the ETL may need a specialisation of etl::iterator_traits for std::common_iterator.

https://en.cppreference.com/w/cpp/iterator/common_iterator/iterator_traits

[StjerneIdioten]

I ran into a similar issuing trying to use etl::copy_s with std::counted_iterator. The cppreference page for std::iterator_traits<std::counted_iterator> seems to have more information. This iterator comes with a function for accessing the base iterator, so I used that whenever I had to interact with ETL functions to get around this.