On 17/05/21 12:17 -0400, Patrick Palka via Libstdc++ wrote:
A range being a random access range is not a sufficient condition for
ranges::next(iter, sent) to have constant time complexity; the range
must also have a sized sentinel. This adjusts the memoization condition
for reverse_view accordingly.
Tested on x86_64-pc-linxu-gnu, does this look OK for trunk? Doesn't
seem to be worth backporting.
OK for trunk. I agree the backports probably aren't needed, but if
it causes anybody problems we can do it later.
libstdc++-v3/ChangeLog:
* include/std/ranges (reverse_view::_S_needs_cached_begin):
Set to false if the underlying non-common random-access range
doesn't have a sized sentinel.
---
libstdc++-v3/include/std/ranges | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index bf52074ca05..e93469ca3b4 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -3340,7 +3340,9 @@ namespace views::__adaptor
{
private:
static constexpr bool _S_needs_cached_begin
- = !common_range<_Vp> && !random_access_range<_Vp>;
+ = !common_range<_Vp> && !(random_access_range<_Vp>
+ && sized_sentinel_for<sentinel_t<_Vp>,
+ iterator_t<_Vp>>);
[[no_unique_address]]
__detail::__maybe_present_t<_S_needs_cached_begin,
--
2.31.1.621.g97eea85a0a
