tdesktop/Telegram/lib_base/base/index_based_iterator.h

// 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