Hi all, I have a vector<pair<bool, int>> from which I need to read (and possibly write) only the vector elements for which the boolean value of the pair is true. I am using boost range filter and reverse adaptors to do that. However, I noticed that the order of the adaptors, ie whether I use reversed | filtered or filtered | reversed produces different results. In fact, for the latter when I use an iterator to the transformed range to change the boolean value of the pair, then the iterator after the change points to a different vector element. This does not happen when I use reversed | filtered. Below is the code demonstrating the issue. Any ideas as to why this is happening are much appreciated! #include <boost/range/adaptors.hpp> #include <vector> #include <utility> #include <iostream> using namespace boost::adaptors; using container_type = std::vector<std::pair<bool,int>>; struct to_include { bool operator()(const std::pair<bool,int>& x) { return x.first; } }; int main() { container_type container; /* element0: 1, 1 */ /* element1: 1, 2 */ /* element2: 1, 3 */ for(size_t i=0; i!=3; ++i) container.push_back(std::make_pair(true, i+1)); container_type container_cpy = container; /* filter and then reverse */ auto fr = container | filtered(to_include()) | reversed; auto fr_it1 = fr.begin(); auto fr_it2 = std::next(fr_it1); fr_it2->first = false; std::cout << "FILTER AND THEN REVERSE\n"; std::cout << fr_it2->first << " " << fr_it2->second << '\n'; /* prints (1,1) instead of (0,2) */ /* reverse and then filter */ auto rf = container_cpy | reversed | filtered(to_include()); auto rf_it1 = rf.begin(); auto rf_it2 = std::next(rf_it1); rf_it2->first = false; std::cout << "\nREVERSE AND THEN FILTER\n"; std::cout << rf_it2->first << " " << rf_it2->second << '\n'; /* prints (0,2) */ return 0; }