at_index.hpp

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// This file is part of the Acts project.
//
// Copyright (C) 2016-2018 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
namespace Acts {
namespace detail {
template <typename T, size_t index, T... values>
struct at_index;

template <typename T, size_t index, T next, T... others>
struct at_index<T, index, next, others...> {
  static constexpr T value = at_index<T, index - 1, others...>::value;
};

template <typename T, T next, T... others>
struct at_index<T, 0, next, others...> {
  static constexpr T value = next;
};
}  // namespace detail
}  // namespace Acts