Question

Using Boost 1_33_1, I get an error implying that my iterator is a const iterator (because it wont let me deref the result from find()).

$ g++ bmi_iter_tst.cpp 
bmi_iter_tst.cpp: In function ‘void tst(employee_set&)’:
bmi_iter_tst.cpp:32: error: invalid initialization of reference of type ‘employee&’ from expression of type ‘const employee’

I know I am not supposed to modify any of the key values, and I don’t, but I still need non-const acces sto modify other data in the container elements.

I know I have done this successfully elsewhere, I just can’t see what would make this const.

The code below is derived from the original boost::multi_index example

#include <boost/multi_index_container.hpp>
#include <boost/multi_index/member.hpp>
#include <boost/multi_index/ordered_index.hpp>


using boost::multi_index_container;
using namespace boost::multi_index;

struct employee
{
  int         id;
  int         tst;

  employee(int id_):id(id_), tst(0){}
};


struct id{};


typedef multi_index_container<
  employee,
  indexed_by<
    ordered_unique<
      tag<id>,  BOOST_MULTI_INDEX_MEMBER(employee,int,id)> >
> employee_set;


void tst(employee_set& s)
{
  employee_set::index_iterator<id>::type it = s.get<id>().find(11);
  employee& eref = *it;

  eref.tst++;
}

Answer 1

From the MultiIndex docs on random access indices:

As usual in Boost.MultiIndex, elements of random access indices are
immutable and can only be modified through member functions replace
and modify. This precludes the usage of many mutating algorithms that
are nonetheless applicable to std::vectors.

This applies to ordered indexes as well.