util/IntrusiveForwardList: add option cache_last

test/util/TestIntrusiveForwardList.cxx

@@ -16,7 +16,7 @@ struct CharItem final : IntrusiveForwardListHook {
 };
 
 static std::string
-ToString(const IntrusiveForwardList<CharItem> &list) noexcept
+ToString(const auto &list) noexcept
 {
 	std::string result;
 	for (const auto &i : list)
@@ -50,3 +50,89 @@ TEST(IntrusiveForwardList, Basic)
 	list.reverse();
 	ASSERT_EQ(ToString(list), "cb");
 }
+
+TEST(IntrusiveForwardList, CacheLast)
+{
+	using Item = CharItem;
+
+	Item items[]{'a', 'b', 'c'};
+
+	using List =IntrusiveForwardList<
+		CharItem, IntrusiveForwardListBaseHookTraits<CharItem>,
+		IntrusiveForwardListOptions{.cache_last = true}>;
+	List list;
+	ASSERT_EQ(ToString(list), "");
+	list.reverse();
+	ASSERT_EQ(ToString(list), "");
+
+	for (auto &i : items)
+		list.push_front(i);
+
+	ASSERT_EQ(ToString(list), "cba");
+	ASSERT_EQ(&list.back(), &items[0]);
+
+	list.erase_after(list.begin());
+	ASSERT_EQ(ToString(list), "ca");
+	ASSERT_EQ(&list.back(), &items[0]);
+
+	list.reverse();
+	ASSERT_EQ(ToString(list), "ac");
+	ASSERT_EQ(&list.back(), &items[2]);
+
+	list.erase_after(list.begin());
+	ASSERT_EQ(ToString(list), "a");
+	ASSERT_EQ(&list.back(), &items[0]);
+
+	list.reverse();
+	ASSERT_EQ(ToString(list), "a");
+	ASSERT_EQ(&list.back(), &items[0]);
+
+	list.pop_front();
+	ASSERT_EQ(ToString(list), "");
+
+	list.insert_after(list.before_begin(), items[0]);
+	ASSERT_EQ(ToString(list), "a");
+	ASSERT_EQ(&list.back(), &items[0]);
+
+	list.insert_after(list.before_begin(), items[1]);
+	ASSERT_EQ(ToString(list), "ba");
+	ASSERT_EQ(&list.back(), &items[0]);
+
+	list.pop_front();
+	ASSERT_EQ(ToString(list), "a");
+	ASSERT_EQ(&list.back(), &items[0]);
+
+	list.pop_front();
+	ASSERT_EQ(ToString(list), "");
+
+	for (auto &i : items)
+		list.push_back(i);
+
+	ASSERT_EQ(ToString(list), "abc");
+	ASSERT_EQ(&list.back(), &items[2]);
+
+	/* move constructor */
+	auto list2 = std::move(list);
+	ASSERT_EQ(ToString(list2), "abc");
+	ASSERT_EQ(&list2.back(), &items[2]);
+	ASSERT_EQ(ToString(list), "");
+
+	/* move operator */
+	list = std::move(list2);
+	ASSERT_EQ(ToString(list), "abc");
+	ASSERT_EQ(&list.back(), &items[2]);
+	ASSERT_EQ(ToString(list2), "");
+
+	list.erase_after(list.begin());
+	ASSERT_EQ(ToString(list), "ac");
+	ASSERT_EQ(&list.back(), &items[2]);
+
+	list.erase_after(list.before_begin());
+	ASSERT_EQ(ToString(list), "c");
+	ASSERT_EQ(&list.back(), &items[2]);
+
+	// insert_after()
+	list.insert_after(list.begin(), items[0]);
+	ASSERT_EQ(ToString(list), "ca");
+	ASSERT_EQ(&list.back(), &items[0]);
+}