Enumerate.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>
#include <utility>

namespace Acts {
template <typename container_type,
          typename container_type_iter =
              decltype(std::begin(std::declval<container_type>())),
          typename = decltype(std::end(std::declval<container_type>()))>
constexpr auto enumerate(container_type &&iterable) {
  struct iterator {
    std::size_t i;
    container_type_iter iter;

    bool operator!=(const iterator &rhs) const { return iter != rhs.iter; }

    void operator++() {
      ++i;
      ++iter;
    }

    auto operator*() const { return std::tie(i, *iter); }
  };
  struct iterable_wrapper {
    container_type iterable;
    auto begin() { return iterator{0, std::begin(iterable)}; }
    auto end() { return iterator{0, std::end(iterable)}; }
  };
  return iterable_wrapper{std::forward<container_type>(iterable)};
}

}  // namespace Acts