Add ranges support to optional

README.md

@@ -901,19 +901,21 @@ Description
 
 #### `<optional>`
 
-  |                       | Introduced  | Revision              |
-  |-----------------------|-------------|-----------------------|
-  | `optional`            | ![][c17ok]  | ![][c23ok] ![][c26no] |
-  | `bad_optional_access` | ![][c17ok]  |                       |
-  | `std::hash<optional>` | ![][c17ok]  |                       |
-  | `nullopt`             | ![][c17ok]* |                       |
-  | `nullopt_t`           | ![][c17ok]* |                       |
-  | `swap(optional)`      | ![][c17ok]  |                       |
-  | `make_optional`       | ![][c17ok]  |                       |
+  |                       | Introduced  | Revision               |
+  |-----------------------|-------------|------------------------|
+  | `optional`            | ![][c17ok]  | ![][c23ok] ![][c26ok]* |
+  | `bad_optional_access` | ![][c17ok]  |                        |
+  | `std::hash<optional>` | ![][c17ok]  |                        |
+  | `nullopt`             | ![][c17ok]* |                        |
+  | `nullopt_t`           | ![][c17ok]* |                        |
+  | `swap(optional)`      | ![][c17ok]  |                        |
+  | `make_optional`       | ![][c17ok]  |                        |
 
 * Notes
   * `nullopt`, `nullopt_t`
     * `std::nullopt` is used if available, `preview::nullopt` otherwise.
+  * C++26
+    * [P3168 (R2)](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p3168r2.html)
 
 #### `<random>`
 

include/preview/__iterator/pointer_iterator.h

@@ -0,0 +1,88 @@
+//
+// Created by yonggyulee on 2024. 10. 20.
+//
+
+#ifndef PREVIEW_ITERATOR_POINTER_ITERATOR_H_
+#define PREVIEW_ITERATOR_POINTER_ITERATOR_H_
+
+#include <cstddef>
+#include <type_traits>
+
+#include "preview/__iterator/detail/contiguous_iterator_tag.h"
+#include "preview/__iterator/iterator_tag.h"
+
+namespace preview {
+namespace detail {
+
+template<typename T, typename Tag = void>
+class pointer_iterator {
+ public:
+  using difference_type = std::ptrdiff_t;
+  using value_type      = std::remove_cv_t<T>;
+  using pointer         = T*;
+  using reference       = T&;
+  using iterator_category = std::random_access_iterator_tag;
+  using iterator_concept  = contiguous_iterator_tag;
+
+  pointer_iterator() = default;
+
+  constexpr pointer_iterator(pointer p)
+      : ptr_(p) {}
+
+  constexpr reference operator*() const noexcept { return *ptr_; }
+  constexpr pointer operator->() const noexcept { return ptr_; }
+
+  constexpr reference operator[](difference_type n) const noexcept {
+    return ptr_[n];
+  }
+
+  constexpr pointer_iterator& operator++() noexcept {
+    ++ptr_;
+    return *this;
+  }
+  constexpr pointer_iterator operator++(int) noexcept {
+    pointer_iterator temp{*this};
+    ++*this;
+    return temp;
+  }
+
+  constexpr pointer_iterator& operator--() noexcept {
+    --ptr_;
+    return *this;
+  }
+  constexpr pointer_iterator operator--(int) noexcept {
+    pointer_iterator temp{*this};
+    --*this;
+    return temp;
+  }
+
+  constexpr pointer_iterator& operator+=(difference_type n) const noexcept {
+    ptr_ += n;
+    return *this;
+  }
+
+  constexpr pointer_iterator& operator-=(difference_type n) const noexcept {
+    ptr_ -= n;
+    return *this;
+  }
+
+  friend constexpr bool operator==(pointer_iterator x, pointer_iterator y) noexcept { return x.ptr_ == y.ptr_; }
+  friend constexpr bool operator!=(pointer_iterator x, pointer_iterator y) noexcept { return x.ptr_ != y.ptr_; }
+  friend constexpr bool operator< (pointer_iterator x, pointer_iterator y) noexcept { return x.ptr_ <  y.ptr_; }
+  friend constexpr bool operator<=(pointer_iterator x, pointer_iterator y) noexcept { return x.ptr_ <= y.ptr_; }
+  friend constexpr bool operator> (pointer_iterator x, pointer_iterator y) noexcept { return x.ptr_ >  y.ptr_; }
+  friend constexpr bool operator>=(pointer_iterator x, pointer_iterator y) noexcept { return x.ptr_ >= y.ptr_; }
+
+  friend constexpr pointer_iterator operator+(pointer_iterator i, difference_type n) noexcept { return pointer_iterator{i.ptr_ + n}; }
+  friend constexpr pointer_iterator operator+(difference_type n, pointer_iterator i) noexcept { return pointer_iterator{i.ptr_ + n}; }
+  friend constexpr pointer_iterator operator-(pointer_iterator i, difference_type n) noexcept { return pointer_iterator{i.ptr_ - n}; }
+  friend constexpr difference_type operator-(pointer_iterator x, pointer_iterator y) noexcept { return x.ptr_ - y.ptr_; }
+
+ private:
+  pointer ptr_ = nullptr;
+};
+
+} // namespace detail
+} // namespace preview
+
+#endif // PREVIEW_ITERATOR_POINTER_ITERATOR_H_

include/preview/__optional/optional.h

@@ -14,12 +14,15 @@
 # include "preview/__concepts/invocable.h"
 # include "preview/__concepts/move_constructible.h"
 # include "preview/__functional/invoke.h"
+# include "preview/__iterator/basic_const_iterator.h"
+# include "preview/__iterator/pointer_iterator.h"
 # include "preview/__memory/addressof.h"
 # include "preview/__memory/construct_at.h"
 # include "preview/__memory/destroy_at.h"
 # include "preview/__optional/bad_optional_access.h"
 # include "preview/__optional/nullopt_t.h"
 # include "preview/__optional/swap.h"
+# include "preview/__ranges/enable_view.h"
 # include "preview/__type_traits/detail/control_special.h"
 # include "preview/__type_traits/is_swappable.h"
 # include "preview/__type_traits/is_invocable.h"
@@ -249,7 +252,9 @@ class optional : private detail::optional_control_smf<T> {
   using base::base;
 
  public:
-  using value_type = T;
+  using value_type     = T;
+  using iterator       = detail::pointer_iterator<T, class optional_iterator_tag>;
+  using const_iterator = detail::pointer_iterator<const T, class optional_iterator_tag>;
 
   static_assert(!std::is_reference<T>::value,
                 "preview::optional : T must not be a reference type");
@@ -600,6 +605,20 @@ class optional : private detail::optional_control_smf<T> {
     this->construct_with(ilist, std::forward<Args>(args)...);
     return **this;
   }
+
+  constexpr iterator begin() noexcept {
+    return iterator{has_value() ? preview::addressof(**this) : nullptr};
+  }
+  constexpr const_iterator begin() const noexcept {
+    return const_iterator{has_value() ? preview::addressof(**this) : nullptr};
+  }
+
+  constexpr iterator end() noexcept {
+    return begin() + has_value();
+  }
+  constexpr const_iterator end() const noexcept {
+    return begin() + has_value();
+  }
 };
 
 # if PREVIEW_CXX_VERSION >= 17
@@ -808,6 +827,16 @@ constexpr inline bool operator>=(const T& value, const optional<U>& opt) {
   return bool(opt) ? value >= *opt : true;
 }
 
+
+// ranges support
+namespace ranges {
+
+template<typename T>
+struct enable_view<optional<T>> : std::true_type {};
+
+// TODO: Specialize format_kind
+
+} // namespace ranges
 } // namespace preview
 
 # endif // PREVIEW_OPTIONAL_OPTIONAL_H_

test/optional/optional_test.cc

@@ -371,3 +371,24 @@ TEST(VERSIONED(optional), copy_over_move) {
   std::swap(op1, op2); // copy is selected for non-movable object
   EXPECT_EQ(NoMove::copied, 2);
 }
+
+TEST(VERSIONED(optional), ranges) {
+  preview::optional<int> o;
+  using I = decltype(o)::iterator;
+  using CI = decltype(o)::const_iterator;
+
+  EXPECT_TRUE_TYPE(preview::contiguous_iterator<I>);
+  EXPECT_TRUE_TYPE(preview::ranges::view<decltype(o)>);
+  EXPECT_EQ(o.begin(), o.begin());
+  EXPECT_EQ(o.begin(), o.end());
+  EXPECT_EQ(o.end(), o.end());
+  EXPECT_EQ(preview::ranges::size(o), 0);
+
+  o = 100;
+  EXPECT_EQ(o.begin(), o.begin());
+  EXPECT_NE(o.begin(), o.end());
+  EXPECT_EQ(o.end(), o.end());
+  EXPECT_EQ(o.begin() + 1, o.end());
+  EXPECT_EQ(o.begin(), o.end() - 1);
+  EXPECT_EQ(preview::ranges::size(o), 1);
+}