Zip.hpp

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// This file is part of the Acts project.
//
// Copyright (C) 2022 CERN for the benefit of the Acts project
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

#pragma once

#include <tuple>

namespace Acts {

template <typename... R>
auto zip(R &&...r) {
  struct It {
    std::tuple<decltype(r.begin())...> iterators;
    static_assert(std::tuple_size_v<decltype(iterators)> > 0);

    using reference = std::tuple<decltype(*r.begin())...>;

    auto operator++() {
      std::apply([](auto &...args) { (++args, ...); }, iterators);
      return *this;
    }

    auto operator!=(const It &other) const {
      return std::get<0>(iterators) != std::get<0>(other.iterators);
    }

    reference operator*() {
      return std::apply([](auto &...args) { return reference{*args...}; },
                        iterators);
    }
  };

  struct Zip {
    It b, e;

    auto begin() { return b; }
    auto end() { return e; }
  };

  auto begin = std::make_tuple(r.begin()...);
  auto end = std::make_tuple(r.end()...);
  return Zip{It{begin}, It{end}};
}

}  // namespace Acts