id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
13094	boost::adaptors::transform fails to preserve bidirectional behavior of range	Jake Cobb <jake.cobb@…>	Neil Groves	"The documentation of `boost::adaptors::transform` states the returned range type is the same as the argument range type.  However, when wrapping `std::vector`, the iterators returned are not bidirectional as the `std::vector` iterators are.  `std::advance` with a negative integer leaves them unchanged and `std::prev` fails to compile with them.  They do work as expected with `operator-`.

{{{#!c++
#include <iostream>
#include <vector>
#include <iterator>
#include <boost/range/adaptor/transformed.hpp>

int main() {
    std::vector<int> data{1,2,3};
    auto transformed = boost::adaptors::transform(data, [](int x) { return x; });
    auto iter = transformed.begin();
    // auto iter = data.begin(); // swap to compare
    std::cout << ""begin: "" << *iter << std::endl; // prints 1 both cases
    std::advance(iter, 1);
    std::cout << ""begin+1: "" << *iter << std::endl; // prints 2 both cases
    std::advance(iter, -1);
    // prints 2 for boost adaptor, 1 for std::vector
    std::cout << ""begin+1-1: "" << *iter << std::endl;
    std::cout << ""begin+1-1 (v2): "" << *(iter - 1) << std::endl; // prints 1 both cases
    // std::prev(iter); // boost fails bidirectional test, won't compile
    return 0;
}
}}}"	Bugs	closed	To Be Determined	range	Boost 1.64.0	Problem	invalid	range adaptors transform