Use type aliases from base class (iterator_interface)

include/Beman/Optional26/detail/iterator.hpp

@@ -11,27 +11,37 @@
 
 namespace beman::optional::detail {
 
+// Forward declaration.
+template <class T, class Container>
+struct contiguous_iterator;
+
+// Base class for contiguous iterator types with Boost stl_interfaces library.
+// Current implementation based on P2727R4: std::iterator_interface.
+template <class T, class Container>
+using base_contiguous_iterator = stl_interfaces::iterator_interface<
+#if !BEMAN_OPTIONAL26_DETAIL_STL_INTERFACES_USE_DEDUCED_THIS
+    contiguous_iterator<T, Container>, // Required for P2727R4 to work with C++20/C++23. TODO: Do more experiments.
+#endif
+    std::contiguous_iterator_tag,
+    T>;
+
 // This is a minimal contiguous iterator.  It uses stl_interfaces library from Boost
 // (current implementation based on https://wg21.link/P2727R4).
 //
-// TODO: Change this to use the stl_interfaces library from Beman when available.
+// TODO: Change this to use the stl_interfaces library from Beman if/when available.
 //
 // @tparam T - The type of the elements the iterator points to.
 // @tparam Container - The type of the container the iterator points to. This parameter exists solely so that different
 // containers using this template can instantiate different types, even if the T parameter is the same.
 template <class T, class Container>
-struct contiguous_iterator : stl_interfaces::iterator_interface<
-#if !BEMAN_OPTIONAL26_DETAIL_STL_INTERFACES_USE_DEDUCED_THIS
-                                 contiguous_iterator<T, Container>,
-#endif
-                                 std::contiguous_iterator_tag,
-                                 T> {
-    using iterator_type     = T*;
-    using difference_type   = std::iterator_traits<iterator_type>::difference_type;
-    using reference         = std::iterator_traits<iterator_type>::reference;
-    using pointer           = std::iterator_traits<iterator_type>::pointer;
-
-    static_assert(std::contiguous_iterator<iterator_type>);
+struct contiguous_iterator : public base_contiguous_iterator<T, Container> {
+    // Alias for the base class.
+    using base_type = base_contiguous_iterator<T, Container>;
+    // Alias for types from the base class.
+    using typename base_type::difference_type;
+    using typename base_type::iterator_category;
+    using typename base_type::pointer;
+    using typename base_type::reference;
 
     // Default constructor.
     contiguous_iterator() noexcept : m_current() {}