feat: add last to iterator interface

include/rusty_iterators/concepts.hpp

@@ -60,6 +60,9 @@ concept InspectFunctor = requires(Functor f, T& t) {
 template <class T, class Functor>
 concept PositionFunctor = AllFunctor<T, Functor>;
 
+template <class T, class Functor>
+concept ReduceFunctor = FoldFunctor<T, T, Functor>;
+
 template <class T>
 concept Summable = requires(T first, T second) {
     { first + second } -> std::same_as<T>;

include/rusty_iterators/interface.hpp

@@ -30,6 +30,7 @@ using concepts::Indexable;
 using concepts::InspectFunctor;
 using concepts::NeFunctor;
 using concepts::PositionFunctor;
+using concepts::ReduceFunctor;
 using concepts::Summable;
 using concepts::TryFoldFunctor;
 using concepts::TupleLike;
@@ -115,6 +116,8 @@ class IterInterface
         requires InspectFunctor<T, Functor>
     auto inspect(Functor&& f) -> Inspect<T, Functor, Derived>;
 
+    [[nodiscard]] auto last() -> std::optional<T>;
+
     template <class Functor>
         requires std::invocable<Functor, T&&>
     [[nodiscard]] auto map(Functor&& f) -> Map<T, Functor, Derived>;
@@ -143,7 +146,7 @@ class IterInterface
     [[nodiscard]] auto position(Functor&& f) -> std::optional<size_t>;
 
     template <class Functor>
-        requires FoldFunctor<T, T, Functor>
+        requires ReduceFunctor<T, Functor>
     [[nodiscard]] auto reduce(Functor&& f) -> std::optional<T>;
 
     template <class R = T>
@@ -342,6 +345,12 @@ auto rusty_iterators::interface::IterInterface<T, Derived>::inspect(Functor&& f)
     return Inspect<T, Functor, Derived>{std::forward<Derived>(self()), std::forward<Functor>(f)};
 }
 
+template <class T, class Derived>
+auto rusty_iterators::interface::IterInterface<T, Derived>::last() -> std::optional<T>
+{
+    return self().reduce([](auto _, auto x) { return x; });
+}
+
 template <class T, class Derived>
 template <class Functor>
     requires std::invocable<Functor, T&&>
@@ -422,7 +431,7 @@ auto rusty_iterators::interface::IterInterface<T, Derived>::position(Functor&& f
 
 template <class T, class Derived>
 template <class Functor>
-    requires rusty_iterators::concepts::FoldFunctor<T, T, Functor>
+    requires rusty_iterators::concepts::ReduceFunctor<T, Functor>
 auto rusty_iterators::interface::IterInterface<T, Derived>::reduce(Functor&& f) -> std::optional<T>
 {
     auto first = self().next();

tests/iterator.test.cpp

@@ -359,3 +359,19 @@ TEST(TestIterator, TestTryFoldEarlyExit)
 
     ASSERT_EQ(result, 6);
 }
+
+TEST(TestIterator, TestLastOnEmptyIterator)
+{
+    auto vec = std::vector<int>{};
+    auto it  = LazyIterator{vec};
+
+    ASSERT_EQ(it.last(), std::nullopt);
+}
+
+TEST(TestIterator, TestLast)
+{
+    auto vec = std::vector{1, 2, 3};
+    auto it  = LazyIterator{vec};
+
+    ASSERT_EQ(it.last(), 3);
+}