From cac97fe59df0057f88506257f350e9007d94cc7f Mon Sep 17 00:00:00 2001
From: janis <janis@nirgendwo.xyz>
Date: Fri, 1 Jul 2022 01:38:55 +0100
Subject: [PATCH] enumerate fix

---
 include/ranges/enumerate.hpp | 284 +++++++++++++++++++++++++----------
 1 file changed, 206 insertions(+), 78 deletions(-)

diff --git a/include/ranges/enumerate.hpp b/include/ranges/enumerate.hpp
index 4cd558b..39e36c8 100644
--- a/include/ranges/enumerate.hpp
+++ b/include/ranges/enumerate.hpp
@@ -2,125 +2,253 @@
 #include "types.hpp"
 #include <cstddef>
 #include <ranges>
+#include <type_traits>
 #include <xutility>
 
 namespace util {
 namespace rg = std::ranges;
 
-template <rg::range R> struct enumerate_iterator_t {
-  using base = rg::iterator_t<R>;
-  using enumerator_type = std::size_t;
-  using value_type = std::pair<enumerator_type, rg::range_value_t<R>>;
-  using difference_type = std::ptrdiff_t;
-  using reference =
-      std::pair<enumerator_type, std::remove_cv_t<rg::range_reference_t<R>>>;
+template <class R>
+concept simple_view = // exposition only
+    rg::view<R> && rg::range<const R> &&
+    std::same_as<std::ranges::iterator_t<R>,
+                 std::ranges::iterator_t<const R>> &&
+    std::same_as<std::ranges::sentinel_t<R>, std::ranges::sentinel_t<const R>>;
 
-  base base_iter{};
-  enumerator_type enumerator{};
+template <rg::input_range R>
+requires(rg::view<R>) class enumerate_view
+    : public rg::view_interface<enumerate_view<R>> {
+private:
+  R base_ = R();
 
-  enumerate_iterator_t() = default;
-  enumerate_iterator_t(const base &b) : base_iter{b}, enumerator(0) {}
-  enumerate_iterator_t(base &&b) : base_iter{std::move(b)}, enumerator(0) {}
+public:
+  template <bool Const> class iterator;
+  template <bool Const> class sentinel;
 
-  auto constexpr operator==(const enumerate_iterator_t &other) const -> bool {
-    return base_iter == other.base_iter;
+  constexpr enumerate_view() = default;
+  constexpr enumerate_view(R base) : base_(std::move(base)) {}
+
+  constexpr auto size() -> rg::range_difference_t<R>
+  requires(rg::sized_range<R>) { return rg::size(base_); }
+  constexpr auto size() const -> rg::range_difference_t<R>
+  requires(rg::sized_range<const R>) { return rg::size(base_); }
+
+  constexpr auto begin() -> iterator<false> {
+    return iterator<false>{rg::begin(base_), 0};
   }
 
-  template <std::sentinel_for<base> S>
-  auto constexpr operator==(const S &sentinel) const -> bool {
-    return sentinel == base_iter;
+  constexpr auto begin() const -> iterator<true> {
+    return iterator<true>{rg::begin(base_), 0};
   }
 
-  auto constexpr operator<=>(const enumerate_iterator_t &other) const {
-    return base_iter <=> other.base_iter;
+  constexpr auto end() { return sentinel<false>(rg::end(base_)); }
+
+  constexpr auto end() requires(rg::common_range<R> &&rg::sized_range<R>) {
+    return iterator<false>{rg::end(base_),
+                           static_cast<rg::range_difference_t<R>>(size())};
   }
 
-  auto inc_enumerator() -> void { enumerator++; }
-  auto dec_enumerator() -> void { enumerator--; }
-  auto dec_enumerator(const difference_type &n) -> void { enumerator -= n; }
-
-  auto operator++(int) -> enumerate_iterator_t {
-    const auto result = *this;
-    base_iter++;
-    inc_enumerator();
-    return result;
+  constexpr auto end() const requires(rg::range<const R>) {
+    return sentinel<true>{rg::end(base_)};
   }
 
-  auto operator++() -> enumerate_iterator_t & {
-    inc_enumerator();
-    ++base_iter;
-    return (*this);
+  constexpr auto end() const
+      requires(rg::common_range<const R> &&rg::sized_range<R>) {
+    return iterator<true>{rg::end(base_),
+                          static_cast<rg::range_difference_t<R>>(size())};
   }
 
-  auto operator--(int) -> enumerate_iterator_t
-      requires(std::bidirectional_iterator<base>) {
-    const auto result = *this;
-    base_iter--;
-    dec_enumerator();
-    return result;
+  constexpr auto base() const -> R &requires(std::copy_constructible<R>) {
+    return base_;
+  }
+  constexpr auto base() -> R && { return std::move(base_); }
+};
+
+template <class R> enumerate_view(R &&) -> enumerate_view<std::views::all_t<R>>;
+
+template <rg::input_range R>
+requires(rg::view<R>) template <bool Const> class enumerate_view<R>::iterator {
+public:
+  using Base = std::conditional_t<Const, const R, R>;
+  using iterator_type = rg::iterator_t<Base>;
+  using iterator_category =
+      typename std::iterator_traits<iterator_type>::iterator_category;
+  using iterator_concept = iterator_category;
+
+  using difference_type = typename rg::range_difference_t<Base>;
+  using enumerator_type = difference_type;
+
+  struct result {
+    const enumerator_type index;
+    rg::range_reference_t<Base> value;
+  };
+
+  using reference = result;
+  using value_type = result;
+
+public:
+  enumerator_type index_ = {};
+  iterator_type base_ = iterator_type();
+
+  iterator() = default;
+  constexpr explicit iterator(iterator_type base, enumerator_type index = 0)
+      : base_(std::move(base)), index_(index) {}
+  constexpr iterator(iterator<!Const> i) requires Const
+      && std::convertible_to<rg::iterator_t<R>, rg::iterator_t<Base>>
+      : base_(std::move(i.base_)), index_(std::move(i.index_)) {}
+
+  constexpr rg::iterator_t<Base>
+  base() const &requires std::copyable<rg::iterator_t<Base>> {
+    return base_;
+  }
+  constexpr rg::iterator_t<Base> base() && { return std::move(base_); }
+
+  constexpr decltype(auto) operator*() const { return result{index_, *base_}; }
+
+  constexpr auto operator++() -> iterator & {
+    ++index_;
+    ++base_;
+    return *this;
   }
 
-  auto operator--()
-      -> enumerate_iterator_t &requires(std::bidirectional_iterator<base>) {
-    dec_enumerator();
-    --base_iter;
-    return (*this);
+  constexpr auto operator++(int) -> void requires(!rg::forward_range<Base>) {
+    ++index_;
+    ++base_;
   }
 
-  auto constexpr operator+(const difference_type &n) const
-      -> enumerate_iterator_t {
-    auto ret = *this;
-    ret.inc_enumerator(n);
-    base_iter += n;
-
-    return ret;
+  constexpr auto operator++(int) -> iterator requires(rg::forward_range<Base>) {
+    const auto tmp = *this;
+    ++index_;
+    ++base_;
+    return tmp;
   }
 
-  auto operator*() -> reference { return reference(enumerator, *base_iter); }
-  auto operator*() const -> reference {
-    return reference(enumerator, *base_iter);
+  constexpr auto operator--()
+      -> iterator &requires(rg::bidirectional_range<Base>) {
+    --index_;
+    --base_;
+    return *this;
+  }
+
+  constexpr auto operator--(int) -> iterator
+      requires(rg::bidirectional_range<Base>) {
+    const auto tmp = *this;
+    --index_;
+    --base_;
+    return tmp;
+  }
+
+  constexpr auto operator+=(difference_type n)
+      -> iterator &requires(rg::random_access_range<Base>) {
+    index_ += n;
+    base_ += n;
+    return *this;
+  }
+
+  constexpr auto operator-=(difference_type n)
+      -> iterator &requires(rg::random_access_range<Base>) {
+    index_ -= n;
+    base_ -= n;
+    return *this;
+  }
+
+  friend constexpr auto operator==(const iterator &lhs, const iterator &rhs)
+      -> bool requires(std::equality_comparable<rg::iterator_t<Base>>) {
+    return lhs.base_ == rhs.base_;
+  }
+
+  friend constexpr auto operator<(const iterator &lhs, const iterator &rhs)
+      -> bool requires(rg::random_access_range<Base>) {
+    return lhs.base_ < rhs.base_;
+  }
+  friend constexpr auto operator>(const iterator &lhs, const iterator &rhs)
+      -> bool requires(rg::random_access_range<Base>) {
+    return rhs < lhs;
+  }
+  friend constexpr auto operator<=(const iterator &lhs, const iterator &rhs)
+      -> bool requires(rg::random_access_range<Base>) {
+    return !(rhs < lhs);
+  }
+  friend constexpr auto operator>=(const iterator &lhs, const iterator &rhs)
+      -> bool requires(rg::random_access_range<Base>) {
+    return !(lhs < rhs);
+  }
+
+  friend constexpr auto operator<=>(
+      const iterator &lhs,
+      const iterator &rhs) requires(std::three_way_comparable<iterator_type>) {
+    return lhs.base_ <=> rhs.base_;
+  }
+
+  friend constexpr auto operator+(const iterator &lhs, difference_type n)
+      -> iterator requires(rg::random_access_range<Base>) {
+    return iterator{lhs} + n;
+  }
+
+  friend constexpr auto operator+(difference_type n, const iterator &rhs)
+      -> iterator requires(rg::random_access_range<Base>) {
+    return n + rhs;
+  }
+
+  friend constexpr auto operator-(const iterator &lhs, difference_type n)
+      -> iterator requires(rg::random_access_range<Base>) {
+    return iterator{lhs} -= n;
+  }
+
+  friend constexpr auto operator-(const iterator &lhs, const iterator &rhs)
+      -> iterator requires(rg::random_access_range<Base>) {
+    return lhs.base_ - rhs.base_;
   }
 };
 
-template <rg::range R>
-class enumerate_view : public rg::view_interface<enumerate_view<R>> {
-  isize enumerator{};
-  enumerate_iterator_t<R> iter_;
-  enumerate_iterator_t<R> end_;
+template <rg::input_range R>
+requires(rg::view<R>) template <bool Const> class enumerate_view<R>::sentinel {
+private:
+  using Base = std::conditional_t<Const, const R, R>;
+  rg::sentinel_t<Base> end_ = rg::sentinel_t<Base>();
 
 public:
-  enumerate_view() = default;
+  sentinel() = default;
+  constexpr explicit sentinel(rg::sentinel_t<Base> end) : end_(end) {}
+  constexpr sentinel(sentinel<!Const> other) requires Const
+      && std::convertible_to<rg::sentinel_t<R>, rg::sentinel_t<Base>>
+      : end_(std::move(other.end_)) {}
 
-  constexpr enumerate_view(R base)
-      : iter_(std::begin(base)), end_(std::end(base)) {}
+  constexpr auto base() const -> rg::sentinel_t<Base> { return end_; }
 
-  constexpr auto begin() const { return iter_; }
-  constexpr auto end() const { return end_; }
+  friend constexpr auto operator==(const iterator<Const> &rhs,
+                                   const sentinel &lhs) -> bool {
+    return rhs.base_ == lhs.end_;
+  }
+
+  friend constexpr auto operator-(const iterator<Const> &rhs,
+                                  const sentinel &lhs)
+      -> rg::range_difference_t<Base> {
+    return rhs.base_ - lhs.end_;
+  }
+  friend constexpr auto operator-(const sentinel &rhs,
+                                  const iterator<Const> &lhs)
+      -> rg::range_difference_t<Base> {
+    return rhs.end_ - lhs.base_;
+  }
 };
 
 namespace detail {
-struct enumerate_range_adaptor_closure {
-  template <rg::viewable_range R> constexpr auto operator()(R &&r) const {
-    return enumerate_view(std::forward<R>(r));
-  }
-};
 
-struct enumerate_range_adaptor {
-  template <rg::viewable_range R> constexpr auto operator()(R &&r) {
-    return enumerate_view(std::forward<R>(r));
+struct enumerate_view_adaptor {
+  template <typename R> constexpr auto operator()(R &&r) const {
+    return enumerate_view{std::move(r)};
   }
 
-  constexpr auto operator()() { return enumerate_range_adaptor_closure(); }
+  template <rg::range R>
+  constexpr friend auto operator|(R &&rng, const enumerate_view_adaptor &) {
+    return enumerate_view{std::move(rng)};
+  }
 };
-
-template <rg::viewable_range R>
-constexpr auto operator|(R &&r, enumerate_range_adaptor_closure const &a) {
-  return a(std::forward<R>(r));
-}
 } // namespace detail
 
 namespace views {
-inline detail::enumerate_range_adaptor_closure enumerate;
+inline detail::enumerate_view_adaptor enumerate;
 } // namespace views
 
 } // namespace util
\ No newline at end of file