Index.hpp

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// This file is part of the Acts project.
//
// Copyright (C) 2019-2020 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 <cstdint>

#include <boost/container/flat_map.hpp>

namespace ActsExamples {

using Index = uint32_t;

template <typename value_t>
using IndexMultimap = boost::container::flat_multimap<Index, value_t>;

template <typename value_t>
inline boost::container::flat_multimap<value_t, Index> invertIndexMultimap(
    const IndexMultimap<value_t>& multimap) {
  using InverseMultimap = boost::container::flat_multimap<value_t, Index>;

  // switch key-value without enforcing the new ordering (linear copy)
  typename InverseMultimap::sequence_type unordered;
  unordered.reserve(multimap.size());
  for (auto&& [index, value] : multimap) {
    // value is now the key and the index is now the value
    unordered.emplace_back(value, index);
  }

  // adopting the unordered sequence will reestablish the correct order
  InverseMultimap inverse;
#if BOOST_VERSION < 107800
  for (const auto& i : unordered) {
    inverse.insert(i);
  }
#else
  inverse.insert(unordered.begin(), unordered.end());
#endif
  return inverse;
}

}  // namespace ActsExamples