When I use views::set_intersection
and views::transform
together in range-v3 v0.12.0, the order of the headers range/v3/view/set_algorithm.hpp
and range/v3/view/transform.hpp
matters. If the former header is included first, the code will not compile. The opposite order compiles well.
This is a minimal example: (see also https://godbolt.org/z/nhK1s3xdv for a live demo)
#include <iostream>
#include <map>
// this order fails to compile, however, switch the order, it compiles
#include <range/v3/view/set_algorithm.hpp>
#include <range/v3/view/transform.hpp>
int main () {
std::map<int, int> m1 {{0, 0}, {1, 1}, {2, 2}};
std::map<int, int> m2 {{0, 0}, {2, 1}, {3, 2}};
{
std::cout << "set_intersection\n";
auto res = ranges::views::set_intersection(m1, m2);
for(auto&& p : res) {
std::cout << p.first << ' ' << p.second << '\n';
}
}
{
std::cout << "set_intersection\n";
auto res = m1 | ranges::views::set_intersection(m2);
for(auto&& p : res) {
std::cout << p.first << ' ' << p.second << '\n';
}
}
{
std::cout << "set_intersection and pipe\n";
auto res = ranges::views::set_intersection(m1, m2)
| ranges::views::transform(
[](auto&& p) { return 0; });
}
return 0;
}
Interestingly, the error message is
error: use of undeclared identifier 'bind_back'
return make_view_closure(bind_back(set_intersection_base_fn{},
for this line
auto res = m1 | ranges::views::set_intersection(m2);
Which is nothing to do with views::transform
.
I searched bind_back
, and it's defined in meta/meta.hpp
, and it's already included in view/set_algorithm.hpp
.
I don't understand where the bug is.
With templates inclusion order matters. range-v3 is heavily templated and it's best not to deviate from the documentation on which headers to include. The bind_back
you found is nested in a namespace meta
. The bind_back
you need is defined in bind_back.hpp, see the range-v3 documentation.