Hi, On Tue, 14 Jul 2026, Yuao Ma wrote:
> Hi! > > On Tue, Jul 14, 2026 at 12:30 PM Patrick Palka <[email protected]> wrote: > > > > For segmented iterators, ranges::distance is equivalent to the sum of > > ranges::distance of each of its segments. > > > > PR libstdc++/123211 > > > > libstdc++-v3/ChangeLog: > > > > * include/bits/ranges_base.h (__distance_fn::operator()): For > > the non-sized-sentinel overload, > > --- > > libstdc++-v3/include/bits/ranges_base.h | 10 ++++++++++ > > 1 file changed, 10 insertions(+) > > > > diff --git a/libstdc++-v3/include/bits/ranges_base.h > > b/libstdc++-v3/include/bits/ranges_base.h > > index ce1c40fc17f6..7f169feaa6b1 100644 > > --- a/libstdc++-v3/include/bits/ranges_base.h > > +++ b/libstdc++-v3/include/bits/ranges_base.h > > @@ -994,6 +994,16 @@ namespace ranges > > constexpr iter_difference_t<_It> > > operator()[[nodiscard]](_It __first, _Sent __last) const > > { > > + if constexpr (__segmented_iterator<_It> && same_as<_It, _Sent>) > > + { > > + iter_difference_t<_It> __n = 0; > > + std::__for_each_segment(__first, __last, [this, &__n](auto > > __first, auto __last) { > > + __n += iter_difference_t<_It>(this->operator()(__first, > > __last)); > > + return __last; > > + }); > > + return __n; > > + } > > + > > iter_difference_t<_It> __n = 0; > > while (__first != __last) > > { > > -- > > 2.55.0.141.g55526a1826 > > > > Great to see this optimization into libstdc++! Beyond > ranges::distance, I think there are more algorithms we can optimize > for segmented iterators. I helped implement some of these for libc++, > and I'd love to contribute similar optimizations to libstdc++ too! That'd be great! I don't have any plans to implement more optimizations myself but would happy to review.
