forward_linked_list uses std::default_sentinel as its end iterator.

Author: davidstone

source/containers/forward_linked_list.cpp

@@ -85,11 +85,8 @@ struct [[clang::trivial_abi]] forward_linked_list trivially_relocatable_if_eligi
 	constexpr auto before_begin() -> iterator {
 		return iterator(std::addressof(m_sentinel));
 	}
-	constexpr auto end() const -> const_iterator {
-		return const_iterator(nullptr);
-	}
-	constexpr auto end() -> iterator {
-		return iterator(nullptr);
+	static constexpr auto end() -> std::default_sentinel_t {
+		return std::default_sentinel;
 	}
 
 	constexpr auto mutable_iterator(const_iterator const it) & -> iterator {

source/containers/linked_list_helper.cpp

@@ -89,6 +89,9 @@ struct list_iterator {
 	OPERATORS_ARROW_DEFINITIONS
 
 	friend auto operator==(list_iterator, list_iterator) -> bool = default;
+	friend constexpr auto operator==(list_iterator const lhs, std::default_sentinel_t) -> bool requires(!has_previous<Links>) {
+		return !lhs.m_links;
+	}
 
 	friend constexpr auto operator+(list_iterator const it, bounded::constant_t<1>) {
 		return list_iterator<Container, Links, T>(it.m_links->next);