Tiny C++17 zip ranges utility

LICENSE.txt

Boost Software License - Version 1.0 - August 17th, 2003

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zip.hpp

#include <tuple>
#include <cstddef>

/// \brief A helper for iterating multiple ranges simultaneously, modelled after python's
/// built-in zip() function.
///
/// \code {.cpp}
/// const std::vector<SomeTable>& tables = ...
/// for (auto&& [table, name] : Zip(tables, GetNames())) {
///   static_assert(std::is_same_v<decltype(table), const SomeTable&>);
///   static_assert(std::is_same_v<decltype(name), std::string&>);
///   // temporaries (like a vector of strings) are kept alive for the
///   // duration of a loop and are safely movable).
///   RegisterTableWithName(std::move(name), &table);
/// }
/// \endcode
template <typename Ranges, typename Indices>
struct Zip;

template <typename... Ranges>
Zip(Ranges&&...) -> Zip<std::tuple<Ranges...>, std::index_sequence_for<Ranges...>>;

template <typename... Ranges, size_t... I>
struct Zip<std::tuple<Ranges...>, std::index_sequence<I...>> {
  explicit Zip(Ranges... ranges) : ranges_(std::forward<Ranges>(ranges)...) {}

  std::tuple<Ranges...> ranges_;

  using sentinel = std::tuple<decltype(std::get<I>(ranges_).end())...>;

  struct iterator : std::tuple<decltype(std::get<I>(ranges_).begin())...> {
    using std::tuple<decltype(std::get<I>(ranges_).begin())...>::tuple;

    auto operator*() {
      return std::tuple<decltype(*std::get<I>(*this))...>{*std::get<I>(*this)...};
    }

    iterator& operator++() {
      (++std::get<I>(*this), ...);
      return *this;
    }

    bool operator!=(const sentinel& s) const {
      bool any_iterator_at_end = (... || (std::get<I>(*this) == std::get<I>(s)));
      return not any_iterator_at_end;
    }
  };

  iterator begin() { return {std::get<I>(ranges_).begin()...}; }

  sentinel end() { return {std::get<I>(ranges_).end()...}; }
};