input_or_output_iteratorに対応

include/ns/enumerate_view.hpp

@@ -31,8 +31,22 @@ namespace ns {
     std::size_t count_ = 0;
 
   public:
+    using difference_type = std::ranges::range_difference_t<View>;
+
     constexpr iterator(std::ranges::iterator_t<View> current, std::size_t count)
       : current_(std::move(current)), count_(std::move(count)) {}
+
+    constexpr std::pair<std::size_t, std::ranges::range_reference_t<View>> //
+    operator*() const {
+      return {count_, *current_};
+    }
+
+    constexpr iterator& operator++() {
+      ++current_;
+      ++count_;
+      return *this;
+    }
+    constexpr void operator++(int) { ++*this; }
   };
 
   template <std::ranges::input_range View>

tests/enumerate_view/enumerate_view.cpp

@@ -1,3 +1,50 @@
 #include <catch2/catch_test_macros.hpp>
+#include <ns/enumerate_view.hpp>
+
+// begin test 用の view
+
+template <class T>
+struct test_input_iterator {
+private:
+  T* ptr_ = nullptr;
+
+public:
+  using difference_type = std::ptrdiff_t;
+  using value_type = std::remove_cv_t<T>;
+  using iterator_concept = std::input_iterator_tag;
+  test_input_iterator() = default;
+  constexpr explicit test_input_iterator(T* ptr) : ptr_(std::move(ptr)) {}
+  constexpr decltype(auto) operator*() const { return *ptr_; }
+  constexpr test_input_iterator& operator++() {
+    ++ptr_;
+    return *this;
+  }
+  constexpr void operator++(int) { ++ptr_; }
+  constexpr bool operator==(const test_input_iterator& other) const { return ptr_ == other.ptr_; }
+};
+
+template <class T>
+struct test_view : std::ranges::view_base {
+private:
+  T value{};
+
+public:
+  test_view() = default;
+  constexpr explicit test_view(T v) : value(std::move(v)) {}
+  auto begin() { return test_input_iterator<T>(std::addressof(value)); }
+  auto begin() const { return test_input_iterator<const T>(std::addressof(value)); }
+  auto end() { return test_input_iterator<T>(std::addressof(value) + 1); }
+  auto end() const { return test_input_iterator<const T>(std::addressof(value) + 1); }
+};
+
+static_assert(std::ranges::view<test_view<int>>);
+static_assert(std::ranges::input_range<test_view<int>>);
+static_assert(not std::ranges::forward_range<test_view<int>>);
+
+// end test 用の view
+
+using testing_view = ns::enumerate_view<test_view<int>>;
+// まだ動かない
+// static_assert(std::input_or_output_iterator<std::ranges::iterator_t<testing_view>>);
 
 // TEST_CASE("enumerate_view", "[enumerate_view]") {}