Add useful iterators

include/nvsl/iterator.hh

@@ -0,0 +1,236 @@
+// -*- mode: c++; c-basic-offset: 2; -*-
+
+/**
+ * @file   iterator.hh
+ * @date   janvier 24, 2024
+ * @brief  Implements indices operation
+ *
+ * @license Licensed under the Apache License, Version 2.0 (the "License"); from
+ *          https://github.com/klmr/cpp11-range/
+ */
+
+#pragma once
+
+#include <cmath>
+#include <iterator>
+#include <type_traits>
+
+namespace nvsl {
+
+  namespace detail {
+
+    template <typename T>
+    struct range_iter_base : std::iterator<std::input_iterator_tag, T> {
+      range_iter_base(T current) : current(current) {}
+
+      T operator*() const { return current; }
+
+      T const *operator->() const { return &current; }
+
+      range_iter_base &operator++() {
+        ++current;
+        return *this;
+      }
+
+      range_iter_base operator++(int) {
+        auto copy = *this;
+        ++*this;
+        return copy;
+      }
+
+      bool operator==(range_iter_base const &other) const {
+        return current == other.current;
+      }
+
+      bool operator!=(range_iter_base const &other) const {
+        return not(*this == other);
+      }
+
+    protected:
+      T current;
+    };
+
+  } // namespace detail
+
+  template <typename T>
+  struct step_range_proxy {
+    struct iterator : detail::range_iter_base<T> {
+      iterator(T current, T step)
+          : detail::range_iter_base<T>(current), step_(step) {}
+
+      using detail::range_iter_base<T>::current;
+
+      iterator &operator++() {
+        current += step_;
+        return *this;
+      }
+
+      iterator operator++(int) {
+        auto copy = *this;
+        ++*this;
+        return copy;
+      }
+
+      // Loses commutativity. Iterator-based ranges are simply broken. :-(
+      bool operator==(iterator const &other) const {
+        return step_ > 0 ? current >= other.current : current < other.current;
+      }
+
+      bool operator!=(iterator const &other) const {
+        return not(*this == other);
+      }
+
+      T step_;
+    };
+
+    step_range_proxy(T begin, T end, T step)
+        : begin_(begin, step), end_(end, step) {}
+
+    iterator begin() const { return begin_; }
+
+    iterator end() const { return end_; }
+
+    std::size_t size() const {
+      if (*end_ >= *begin_) {
+        // Increasing and empty range
+        if (begin_.step_ < T{0}) return 0;
+      } else {
+        // Decreasing range
+        if (begin_.step_ > T{0}) return 0;
+      }
+      return std::ceil(
+          std::abs(static_cast<double>(*end_ - *begin_) / begin_.step_));
+    }
+
+  private:
+    iterator begin_;
+    iterator end_;
+  };
+
+  template <typename T>
+  struct range_proxy {
+    struct iterator : detail::range_iter_base<T> {
+      iterator(T current) : detail::range_iter_base<T>(current) {}
+    };
+
+    range_proxy(T begin, T end) : begin_(begin), end_(end) {}
+
+    step_range_proxy<T> step(T step) { return {*begin_, *end_, step}; }
+
+    iterator begin() const { return begin_; }
+
+    iterator end() const { return end_; }
+
+    std::size_t size() const { return *end_ - *begin_; }
+
+  private:
+    iterator begin_;
+    iterator end_;
+  };
+
+  template <typename T>
+  struct step_inf_range_proxy {
+    struct iterator : detail::range_iter_base<T> {
+      iterator(T current = T(), T step = T())
+          : detail::range_iter_base<T>(current), step(step) {}
+
+      using detail::range_iter_base<T>::current;
+
+      iterator &operator++() {
+        current += step;
+        return *this;
+      }
+
+      iterator operator++(int) {
+        auto copy = *this;
+        ++*this;
+        return copy;
+      }
+
+      bool operator==(iterator const &) const { return false; }
+
+      bool operator!=(iterator const &) const { return true; }
+
+    private:
+      T step;
+    };
+
+    step_inf_range_proxy(T begin, T step) : begin_(begin, step) {}
+
+    iterator begin() const { return begin_; }
+
+    iterator end() const { return iterator(); }
+
+  private:
+    iterator begin_;
+  };
+
+  template <typename T>
+  struct infinite_range_proxy {
+    struct iterator : detail::range_iter_base<T> {
+      iterator(T current = T()) : detail::range_iter_base<T>(current) {}
+
+      bool operator==(iterator const &) const { return false; }
+
+      bool operator!=(iterator const &) const { return true; }
+    };
+
+    infinite_range_proxy(T begin) : begin_(begin) {}
+
+    step_inf_range_proxy<T> step(T step) { return {*begin_, step}; }
+
+    iterator begin() const { return begin_; }
+
+    iterator end() const { return iterator(); }
+
+  private:
+    iterator begin_;
+  };
+
+  template <typename T, typename U>
+  auto range(T begin, U end)
+      -> range_proxy<typename std::common_type<T, U>::type> {
+    using C = typename std::common_type<T, U>::type;
+    return {static_cast<C>(begin), static_cast<C>(end)};
+  }
+
+  template <typename T>
+  infinite_range_proxy<T> range(T begin) {
+    return {begin};
+  }
+
+  namespace traits {
+
+    template <typename C>
+    struct has_size {
+      template <typename T>
+      static auto check(T *) -> typename std::is_integral<
+          decltype(std::declval<T const>().size())>::type;
+
+      template <typename>
+      static auto check(...) -> std::false_type;
+
+      using type = decltype(check<C>(0));
+      static constexpr bool value = type::value;
+    };
+
+  } // namespace traits
+
+  template <typename C,
+            typename = typename std::enable_if<traits::has_size<C>::value>>
+  auto indices(C const &cont) -> range_proxy<decltype(cont.size())> {
+    return {0, cont.size()};
+  }
+
+  template <typename T, std::size_t N>
+  range_proxy<std::size_t> indices(T (&)[N]) {
+    return {0, N};
+  }
+
+  template <typename T>
+  range_proxy<typename std::initializer_list<T>::size_type>
+  indices(std::initializer_list<T> &&cont) {
+    return {0, cont.size()};
+  }
+
+} // namespace nvsl