[libcxx-commits] [libcxx] [libc++] optimization on ranges::drop_view::begin (#72883) (PR #72929)

[Will Hawkins via libcxx-commits]

================
@@ -104,7 +108,8 @@ namespace ranges {
     constexpr auto begin() const
       requires random_access_range<const _View> && sized_range<const _View>
     {
-      return ranges::next(ranges::begin(__base_), __count_, ranges::end(__base_));
+      range_difference_t<_View> __dist = ranges::distance(__base_);
+      return ranges::begin(__base_) + std::min(__count_, __dist);
----------------
hawkinsw wrote:

For my own edification, I attempted to answer this question ... it looks like the type is stripped of `const`/`&`?

```C++
template <range _Rp>
using range_difference_t = iter_difference_t<iterator_t<_Rp>>;

// ...

template <class _Ip>
using iter_difference_t = typename conditional_t<__is_primary_template<iterator_traits<remove_cvref_t<_Ip> > >::value,
                                                 incrementable_traits<remove_cvref_t<_Ip> >,
                                                 iterator_traits<remove_cvref_t<_Ip> > >::difference_type;

```



https://github.com/llvm/llvm-project/pull/72929