Implement LWG-3749 common_iterator should handle integer-class diff…

…erence types (#4190)
microsoft · Nov 17, 2023 · d9d2a91 · d9d2a91
1 parent 5abffb6
commit d9d2a91
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Showing 2 changed files with 33 additions and 7 deletions.
diff --git a/stl/inc/iterator b/stl/inc/iterator
@@ -1103,14 +1103,22 @@ concept _Has_forward_category = requires {
  requires derived_from<_Iter_cat_t<_Iter>, forward_iterator_tag>;
 };
 
-template <input_iterator _Iter, class _Se>
-struct iterator_traits<common_iterator<_Iter, _Se>> {
- using iterator_concept = conditional_t<forward_iterator<_Iter>, forward_iterator_tag, input_iterator_tag>;
+template <class _Iter>
+struct _Common_iterator_category_base {};
+
+template <class _Iter>
+ requires is_integral_v<iter_difference_t<_Iter>>
+struct _Common_iterator_category_base<_Iter> {
  using iterator_category = conditional_t<_Has_forward_category<_Iter>, forward_iterator_tag, input_iterator_tag>;
- using value_type = iter_value_t<_Iter>;
- using difference_type = iter_difference_t<_Iter>;
- using pointer = typename _Common_iterator_pointer_type<_Iter, _Se>::pointer;
- using reference = iter_reference_t<_Iter>;
+};
+
+template <input_iterator _Iter, class _Se>
+struct iterator_traits<common_iterator<_Iter, _Se>> : _Common_iterator_category_base<_Iter> {
+ using iterator_concept = conditional_t<forward_iterator<_Iter>, forward_iterator_tag, input_iterator_tag>;
+ using value_type = iter_value_t<_Iter>;
+ using difference_type = iter_difference_t<_Iter>;
+ using pointer = typename _Common_iterator_pointer_type<_Iter, _Se>::pointer;
+ using reference = iter_reference_t<_Iter>;
 };
 
 template <class _Iter>

diff --git a/tests/std/tests/P0896R4_common_iterator/test.cpp b/tests/std/tests/P0896R4_common_iterator/test.cpp
@@ -315,6 +315,24 @@ constexpr bool test_lwg_3574() {
  return true;
 }
 
+template <class It, class Se>
+concept common_iterator_has_iterator_category =
+ requires { typename iterator_traits<common_iterator<It, Se>>::iterator_category; };
+
+// LWG-3749 common_iterator should handle integer-class difference types
+void test_lwg_3749() { // COMPILE-ONLY
+ static_assert(common_iterator_has_iterator_category<int*, const int*>);
+ static_assert(common_iterator_has_iterator_category<int*, unreachable_sentinel_t>);
+
+ using small_unbounded_iota = decltype(views::iota(42));
+ static_assert(common_iterator_has_iterator_category<ranges::iterator_t<small_unbounded_iota>,
+ ranges::sentinel_t<small_unbounded_iota>>);
+
+ using large_unbounded_iota = decltype(views::iota(42ull));
+ static_assert(!common_iterator_has_iterator_category<ranges::iterator_t<large_unbounded_iota>,
+ ranges::sentinel_t<large_unbounded_iota>>);
+}
+
 // Validate that _Variantish works when fed with a non-trivially-destructible type
 void test_non_trivially_destructible_type() { // COMPILE-ONLY
  struct non_trivially_destructible_input_iterator {