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Telegram/lib_base/base/index_based_iterator.h

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+// This file is part of Desktop App Toolkit,
+// a set of libraries for developing nice desktop applications.
+//
+// For license and copyright information please follow this link:
+// https://github.com/desktop-app/legal/blob/master/LEGAL
+//
+#pragma once
+
+#include "base/assertion.h"
+
+namespace base {
+
+template <typename Container>
+class index_based_iterator {
+public:
+	using iterator_category = std::random_access_iterator_tag;
+
+	using value_type = typename Container::value_type;
+	using difference_type = typename Container::difference_type;
+	using pointer = std::conditional_t<
+		std::is_const_v<Container>,
+		typename Container::const_pointer,
+		typename Container::pointer>;
+	using reference = std::conditional_t<
+		std::is_const_v<Container>,
+		typename Container::const_reference,
+		typename Container::reference>;
+	using base_type = std::conditional_t<
+		std::is_const_v<Container>,
+		typename Container::const_iterator,
+		typename Container::iterator>;
+
+	index_based_iterator(Container *container, base_type impl)
+		: _container(container)
+		, _index(impl - _container->begin()) {
+	}
+
+	reference operator*() const {
+		return *(_container->begin() + _index);
+	}
+	pointer operator->() const {
+		return std::addressof(**this);
+	}
+	index_based_iterator &operator++() {
+		++_index;
+		return *this;
+	}
+	index_based_iterator operator++(int) {
+		auto copy = *this;
+		++*this;
+		return copy;
+	}
+	index_based_iterator &operator--() {
+		--_index;
+		return *this;
+	}
+	index_based_iterator operator--(int) {
+		auto copy = *this;
+		--*this;
+		return copy;
+	}
+	index_based_iterator &operator+=(difference_type offset) {
+		_index += offset;
+		return *this;
+	}
+	index_based_iterator operator+(difference_type offset) const {
+		auto copy = *this;
+		copy += offset;
+		return copy;
+	}
+	index_based_iterator &operator-=(difference_type offset) {
+		_index -= offset;
+		return *this;
+	}
+	index_based_iterator operator-(difference_type offset) const {
+		auto copy = *this;
+		copy -= offset;
+		return copy;
+	}
+	difference_type operator-(const index_based_iterator &other) const {
+		return _index - other._index;
+	}
+	reference operator[](difference_type offset) const {
+		return *(*this + offset);
+	}
+
+	bool operator==(const index_based_iterator &other) const {
+		Expects(_container == other._container);
+		return _index == other._index;
+	}
+	bool operator!=(const index_based_iterator &other) const {
+		Expects(_container == other._container);
+		return _index != other._index;
+	}
+	bool operator<(const index_based_iterator &other) const {
+		Expects(_container == other._container);
+		return _index < other._index;
+	}
+	bool operator>(const index_based_iterator &other) const {
+		return other < *this;
+	}
+	bool operator<=(const index_based_iterator &other) const {
+		return !(other < *this);
+	}
+	bool operator>=(const index_based_iterator &other) const {
+		return !(*this < other);
+	}
+
+	base_type base() const {
+		return _container->begin() + _index;
+	}
+
+private:
+	Container *_container = nullptr;
+	difference_type _index = 0;
+
+};
+
+template <typename Container>
+index_based_iterator<Container> index_based_begin(Container &container) {
+	return { &container, std::begin(container) };
+}
+
+template <typename Container>
+index_based_iterator<Container> index_based_end(Container &container) {
+	return { &container, std::end(container) };
+}
+
+} // namespace base