diff --git a/include/iterator.hpp b/include/iterator.hpp
index 949acfa..e46b96b 100644
--- a/include/iterator.hpp
+++ b/include/iterator.hpp
@@ -1,6 +1,11 @@
 #pragma once
 
+#include <compare>
+#include <cstddef>
+#include <iterator>
 #include <tuple>
+#include <type_traits>
+#include <xutility>
 
 namespace util {
 
@@ -32,4 +37,150 @@ class Range {
   auto end() const -> const Iterator { return m_end; }
 };
 
+template <typename V, typename I = V *> struct BaseIterator {
+  using value_type = V;
+  using reference = V &;
+  using difference_type = std::ptrdiff_t;
+
+  I base_iter;
+
+  BaseIterator(const I &iter) : base_iter(iter) {}
+  BaseIterator(I &&iter) : base_iter(std::move(iter)) {}
+};
+
+template <typename V, typename I = V *>
+struct InputOrOutputIterator : public BaseIterator<V, I> {
+  InputOrOutputIterator(const I &iter) : BaseIterator<V, I>(iter) {}
+  InputOrOutputIterator(I &&iter) : BaseIterator<V, I>(std::move(iter)) {}
+
+  auto constexpr operator*() const -> void {}
+
+  auto constexpr operator++(int) -> InputOrOutputIterator {
+    const auto ret = *this;
+    this->base_iter++;
+    return ret;
+  }
+  auto constexpr operator++() -> InputOrOutputIterator & {
+    this ++;
+    return *this;
+  }
+};
+
+template <typename V, typename I = V *>
+struct InputIterator : public InputOrOutputIterator<V, I>,
+                       public std::input_iterator_tag {
+  InputIterator(const I &iter) : BaseIterator<V, I>(iter) {}
+  InputIterator(I &&iter) : BaseIterator<V, I>(std::move(iter)) {}
+
+  auto constexpr operator*() const -> const V & { return *this->base_iter; }
+};
+
+template <typename V, typename I = V *>
+struct OutputIterator : public InputOrOutputIterator<V, I>,
+                        public std::output_iterator_tag {
+  OutputIterator(const I &iter) : BaseIterator<V, I>(iter) {}
+  OutputIterator(I &&iter) : BaseIterator<V, I>(std::move(iter)) {}
+
+  auto constexpr operator*() -> V & { return *this->base_iter; }
+};
+
+template <typename V, typename I = V *>
+struct ForwardIterator : public InputIterator<V, I>,
+                         public std::forward_iterator_tag {
+  ForwardIterator(const I &iter) : BaseIterator<V, I>(iter) {}
+  ForwardIterator(I &&iter) : BaseIterator<V, I>(std::move(iter)) {}
+
+  auto constexpr operator==(const ForwardIterator &rhs) const -> bool {
+    return this->base_iter == rhs.base_iter;
+  }
+};
+
+template <typename V, typename I = V *>
+struct BidirectionalIterator : public ForwardIterator<V, I>,
+                               public std::bidirectional_iterator_tag {
+  BidirectionalIterator(const I &iter) : BaseIterator<V, I>(iter) {}
+  BidirectionalIterator(I &&iter) : BaseIterator<V, I>(std::move(iter)) {}
+
+  auto constexpr operator--(int) -> BidirectionalIterator {
+    const auto ret = *this;
+    this->base_iter--;
+    return ret;
+  }
+  auto constexpr operator--() -> BidirectionalIterator & {
+    this --;
+    return *this;
+  }
+};
+
+template <typename V, typename I = V *>
+struct RandomAccessIterator : public BidirectionalIterator<V, I>,
+                              public std::random_access_iterator_tag {
+  using difference_type = typename BaseIterator<V, I>::difference_type;
+
+  RandomAccessIterator(const I &iter) : BaseIterator<V, I>(iter) {}
+  RandomAccessIterator(I &&iter) : BaseIterator<V, I>(std::move(iter)) {}
+
+  auto constexpr operator<=>(const RandomAccessIterator &rhs) const
+      -> std::strong_ordering {
+    return this->base_iter <=> rhs.base_iter;
+  }
+
+  auto constexpr operator-(const RandomAccessIterator &rhs) const
+      -> difference_type {
+    return this->base_iter - rhs.base_iter;
+  }
+  auto constexpr operator+(const difference_type &n) const
+      -> RandomAccessIterator {
+    return RandomAccessIterator(this->base_iter + n);
+  }
+  friend auto constexpr operator+(const difference_type &n,
+                                  const RandomAccessIterator &rhs)
+      -> RandomAccessIterator {
+    return rhs + n;
+  }
+  auto constexpr operator-(const difference_type &n) const
+      -> RandomAccessIterator {
+    return RandomAccessIterator(this->base_iter - n);
+  }
+
+  auto operator+=(const difference_type &n) -> RandomAccessIterator & {
+    *this = RandomAccessIterator(this->base_iter + n);
+    return *this;
+  }
+  auto operator-=(const difference_type &n) -> RandomAccessIterator & {
+    *this = RandomAccessIterator(this->base_iter - n);
+    return *this;
+  }
+
+  auto constexpr operator[](const difference_type &n) const -> const V & {
+    return this->base_iter[n];
+  }
+  auto operator[](const difference_type &n) -> V & {
+    return this->base_iter[n];
+  }
+};
+
+template <typename I>
+using Iterator = std::conditional_t<
+    std::random_access_iterator<I>,
+    RandomAccessIterator<std::iter_value_t<I>, I>,
+    std::conditional_t<
+        std::bidirectional_iterator<I>,
+        BidirectionalIterator<std::iter_value_t<I>, I>,
+        std::conditional_t<
+            std::forward_iterator<I>, ForwardIterator<std::iter_value_t<I>, I>,
+            std::conditional_t<
+                std::output_iterator<I, decltype(*std::declval<I>())>,
+                OutputIterator<std::iter_value_t<I>, I>,
+                std::conditional_t<
+                    std::input_iterator<I>,
+                    InputIterator<std::iter_value_t<I>, I>,
+                    std::conditional_t<
+                        std::input_or_output_iterator<I>,
+                        InputOrOutputIterator<std::iter_value_t<I>, I>,
+                        RandomAccessIterator<I, I *>>>>>>>;
+
+template <std::ranges::range R>
+using RangeIterator = Iterator<std::ranges::iterator_t<R>>;
+
 }  // namespace util