struct __distance_fn final
{
template<input_or_output_iterator _It, sentinel_for<_It> _Sent>
- [[nodiscard]]
+ requires (!sized_sentinel_for<_Sent, _It>)
constexpr iter_difference_t<_It>
- operator()(_It __first, _Sent __last) const
+ operator()[[nodiscard]](_It __first, _Sent __last) const
{
- if constexpr (sized_sentinel_for<_Sent, _It>)
- return __last - __first;
- else
+ iter_difference_t<_It> __n = 0;
+ while (__first != __last)
{
- iter_difference_t<_It> __n = 0;
- while (__first != __last)
- {
- ++__first;
- ++__n;
- }
- return __n;
+ ++__first;
+ ++__n;
}
+ return __n;
+ }
+
+ template<input_or_output_iterator _It, sized_sentinel_for<_It> _Sent>
+ [[nodiscard]]
+ constexpr iter_difference_t<_It>
+ operator()(const _It& __first, const _Sent& __last) const
+ {
+ return __last - __first;
}
template<range _Range>
--- /dev/null
+// { dg-options "-std=gnu++20" }
+// { dg-do compile { target c++20 } }
+
+#include <iterator>
+
+struct movable_iterator
+{
+ using difference_type = long;
+
+ movable_iterator() = default;
+ movable_iterator(movable_iterator&&) = default;
+ movable_iterator& operator=(movable_iterator&&) = default;
+
+ int operator*() const { return 1; }
+
+ movable_iterator& operator++() { return *this; }
+ void operator++(int) { }
+
+ bool operator==(const movable_iterator&) const = default;
+};
+
+using namespace std;
+
+constexpr counted_iterator<movable_iterator> it({}, 3);
+
+static_assert( sized_sentinel_for<std::default_sentinel_t, counted_iterator<movable_iterator>> );
+// LWG 3392
+// ranges::distance() cannot be used on a move-only iterator
+// with a sized sentinel
+static_assert( ranges::distance(it, default_sentinel) == 3 );