https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112641
Bug ID: 112641
Summary: <ranges>: `drop_view::begin const` has ????(n)
complexity
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: hewillk at gmail dot com
Target Milestone: ---
The wording of `drop_view::begin const` in [range.drop.view] is
Returns: ranges::next(ranges::begin(base_), count_,
ranges::end(base_)).
Note that "returns" is used here, which means that the implementation only
needs to return the value of `ranges::next` and does not need to obtain the
value through `ranges::advance`, which will have 𝒪(n) complexity in the case of
random-access-sized but non-common range.
#include <ranges>
int main() {
const auto s = std::ranges::subrange(std::views::iota(0uz), size_t(-1));
const auto r = std::ranges::drop_view(s, s.size() - 1);
const auto b = r.begin(); // time out
}
https://godbolt.org/z/1KnKKacs8
Thanks to Mr. Jonathan for clarifying this on the LWG mailing list.
