New cpp folder structure

Signed-off-by: Alexander Borsuk <me@alex.bio>

libs/base/range_iterator.hpp

@@ -0,0 +1,100 @@
+#pragma once
+
+#include <iterator>
+#include <type_traits>
+
+namespace base
+{
+// RagneItrator allows to write for loops as follows:
+// for (auto const i : range(N))
+//   ...
+// for (auto const i : range(M, N))
+//   ...
+// And initialize stl containers like this:
+// vector<int> mySequence(MakeRangeIterator(0), MakeRangeIterator(10));
+template <typename TCounter>
+struct RangeIterator
+{
+  explicit RangeIterator(TCounter const current) : m_current(current) {}
+  RangeIterator & operator++() { ++m_current; return *this; }
+  RangeIterator operator++(int) { return RangeIterator(m_current++); }
+  RangeIterator & operator--() { --m_current; return *this; }
+  RangeIterator operator--(int) { return RangeIterator(m_current--); }
+  bool operator==(RangeIterator const & it) const { return m_current == it.m_current; }
+  bool operator!=(RangeIterator const & it) const { return !(*this == it); }
+
+  TCounter operator*() const { return m_current; }
+
+  TCounter m_current;
+};
+}  // namespace base
+
+namespace std
+{
+template <typename T>
+struct iterator_traits<base::RangeIterator<T>>
+{
+  using difference_type = T;
+  using value_type = T;
+  using pointer = void;
+  using reference = T;
+  using iterator_category = std::bidirectional_iterator_tag;
+};
+} // namespace std
+
+namespace base
+{
+template <typename TCounter, bool forward>
+struct RangeWrapper
+{
+  using value_type = std::remove_cv_t<TCounter>;
+  using iterator_base = RangeIterator<value_type>;
+  using iterator = std::conditional_t<forward, iterator_base, std::reverse_iterator<iterator_base>>;
+
+  RangeWrapper(TCounter const from, TCounter const to):
+      m_begin(from),
+      m_end(to)
+  {
+  }
+
+  iterator begin() const { return iterator(iterator_base(m_begin)); }
+  iterator end() const { return iterator(iterator_base(m_end)); }
+
+  value_type const m_begin;
+  value_type const m_end;
+};
+
+// Use this helper to iterate through 0 to `to'.
+template <typename TCounter>
+RangeWrapper<TCounter, true> UpTo(TCounter const to)
+{
+  return {{}, to};
+}
+
+// Use this helper to iterate through `from' to `to'.
+template <typename TCounter>
+RangeWrapper<TCounter, true> UpTo(TCounter const from, TCounter const to)
+{
+  return {from, to};
+}
+
+// Use this helper to iterate through `from' to 0.
+template <typename TCounter>
+RangeWrapper<TCounter, false> DownTo(TCounter const from)
+{
+  return {from, {}};
+}
+
+// Use this helper to iterate through `from' to `to'.
+template <typename TCounter>
+RangeWrapper<TCounter, false> DownTo(TCounter const from, TCounter const to)
+{
+  return {to, from};
+}
+
+template <typename TCounter>
+RangeIterator<TCounter> MakeRangeIterator(TCounter const counter)
+{
+  return RangeIterator<TCounter>(counter);
+}
+}  // namespace base