indirect_iterator_adaptor and const_iterator

From: George A. Heintzelman (georgeh_at_[hidden])
Date: 2001-10-04 14:01:15

Hi boosters,

The following code does not compile with boost 1.25.0:

#include <boost/iterator_adaptors.hpp>
#include <vector>

using namespace boost;
using namespace std;

int main() {
  int ints[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };

  typedef vector<int const *> vect_t;
  vect_t v;
  for (int i = 9; i >=0; i--) {
    v.push_back(ints + i);
  }
  
  typedef indirect_iterator_generator<vect_t::iterator>::type
    indirector;

    
  for (indirector it = indirector(v.begin()), 
                  end = indirector(v.end()); it != end; ++it) {
    const int &ref = *it;
    
    cout << ref << '\n';
  }
}

If I change the typedef to typedef vector<int *> vect_t; it works as 
expected. The same problem holds when const_iterators are used instead
of const int **'s. 

The problem arises because the reference type and pointer type of an
indirected <const int **> are int & and int *, not const int & and const int *.

The following patch fixes the problem ( I think it should be used for
indirect_iterator_pair_generator as well, so both the iterator and 
const_iterator in that case will be for a const x.). I took the liberty of 
renaming the detail::value_of_value_type template to 
detail::traits_of_value_type and using that:

*** /home/georgeh/boost/boost/iterator_adaptors.hpp	Fri Sep 28 09:03:33 2001
--- ./iterator_adaptors.hpp	Thu Oct  4 14:51:17 2001
***************
*** 891,899 ****
  namespace detail {
  # if !defined(BOOST_MSVC) // stragely instantiated even when unused! Maybe try a recursive template someday ;-)
    template <class T>
!   struct value_type_of_value_type {
        typedef typename boost::detail::iterator_traits<T>::value_type outer_value;
!       typedef typename boost::detail::iterator_traits<outer_value>::value_type type;
    };
  # endif
  }
--- 891,901 ----
  namespace detail {
  # if !defined(BOOST_MSVC) // stragely instantiated even when unused! Maybe try a recursive template someday ;-)
    template <class T>
!   struct traits_of_value_type {
        typedef typename boost::detail::iterator_traits<T>::value_type outer_value;
!       typedef typename boost::detail::iterator_traits<outer_value>::value_type value_type;
!       typedef typename boost::detail::iterator_traits<outer_value>::reference reference;
!       typedef typename boost::detail::iterator_traits<outer_value>::pointer pointer;
    };
  # endif
  }
***************
*** 901,911 ****
  template <class OuterIterator,      // Mutable or Immutable, does not matter
            class Value
  #if !defined(BOOST_MSVC)
!                 = BOOST_ARG_DEPENDENT_TYPENAME detail::value_type_of_value_type<OuterIterator>::type
  #endif
!           , class Reference = Value&
            , class Category = BOOST_ARG_DEPENDENT_TYPENAME boost::detail::iterator_traits<OuterIterator>::iterator_category
!           , class Pointer = Value*
           >
  struct indirect_iterator_generator
  {
--- 903,923 ----
  template <class OuterIterator,      // Mutable or Immutable, does not matter
            class Value
  #if !defined(BOOST_MSVC)
!                 = BOOST_ARG_DEPENDENT_TYPENAME detail::traits_of_value_type<OuterIterator>::value_type
  #endif
!           , class Reference 
! #if !defined(BOOST_MSVC)
! 	        = BOOST_ARG_DEPENDENT_TYPENAME detail::traits_of_value_type<OuterIterator>::reference
! #else
!                 = Value &
! #endif
            , class Category = BOOST_ARG_DEPENDENT_TYPENAME boost::detail::iterator_traits<OuterIterator>::iterator_category
!           , class Pointer 
! #if !defined(BOOST_MSVC)
! 	        = BOOST_ARG_DEPENDENT_TYPENAME detail::traits_of_value_type<OuterIterator>::pointer
! #else
! = Value*
! #endif
           >
  struct indirect_iterator_generator
  {
***************
*** 916,927 ****
  template <class OuterIterator,      // Mutable or Immutable, does not matter
            class Value
  #if !defined(BOOST_MSVC)
!                 = BOOST_ARG_DEPENDENT_TYPENAME detail::value_type_of_value_type<OuterIterator>::type
  #endif
!           , class Reference = Value&
            , class ConstReference = const Value&
            , class Category = BOOST_ARG_DEPENDENT_TYPENAME boost::detail::iterator_traits<OuterIterator>::iterator_category
!           , class Pointer = Value*
            , class ConstPointer = const Value*
             >
  struct indirect_iterator_pair_generator
--- 928,949 ----
  template <class OuterIterator,      // Mutable or Immutable, does not matter
            class Value
  #if !defined(BOOST_MSVC)
!                 = BOOST_ARG_DEPENDENT_TYPENAME detail::traits_of_value_type<OuterIterator>::value_type
  #endif
!           , class Reference 
! #if !defined(BOOST_MSVC)
! 	        = BOOST_ARG_DEPENDENT_TYPENAME detail::traits_of_value_type<OuterIterator>::reference
! #else
!                 = Value &
! #endif
            , class ConstReference = const Value&
            , class Category = BOOST_ARG_DEPENDENT_TYPENAME boost::detail::iterator_traits<OuterIterator>::iterator_category
!           , class Pointer 
! #if !defined(BOOST_MSVC)
! 	        = BOOST_ARG_DEPENDENT_TYPENAME detail::traits_of_value_type<OuterIterator>::pointer
! #else
!                 = Value*
! #endif
            , class ConstPointer = const Value*
             >
  struct indirect_iterator_pair_generator