tuple.h

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// -----------------------------------------------------------------------------
//
// Copyright (C) 2021 CERN & University of Surrey for the benefit of the
// BioDynaMo collaboration. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
//
// See the LICENSE file distributed with this work for details.
// See the NOTICE file distributed with this work for additional information
// regarding copyright ownership.
//
// -----------------------------------------------------------------------------
 
#ifndef CORE_UTIL_TUPLE_H_
#define CORE_UTIL_TUPLE_H_
 
#include <type_traits>
#include <utility>
 
namespace bdm {
 
using std::size_t;
 
namespace detail {
// Inspiration taken from:
// https://stackoverflow.com/questions/21062864/optimal-way-to-access-stdtuple-element-in-runtime-by-index
 
template <typename TTuple, typename TFunction, size_t TIndex>
void ApplyImpl(TTuple* t, TFunction&& function) {
  function(&std::get<TIndex>(*t));
}
 
template <typename TTuple, typename TFunction, size_t... TIndices>
void Apply(TTuple* t, size_t index, TFunction&& f,
           std::index_sequence<TIndices...>) {
  using ApplyImplSignature = void(TTuple*, TFunction &&);  // NOLINT
  // create lookup table that maps runtime index to right ApplyImpl function
  static constexpr ApplyImplSignature* kLut[] = {
      &ApplyImpl<TTuple, TFunction, TIndices>...};
  kLut[index](t, f);
}
 
template <typename T, size_t Counter, typename... Types>
struct GetIndexImpl;
 
template <typename T, size_t Counter, typename FirstType>
struct GetIndexImpl<T, Counter, FirstType> {
  int static constexpr GetValue() {
    if (std::is_same<T, FirstType>::value) {
      return Counter;
    } else {
      return -1;
    }
  }
};
 
template <typename T, size_t Counter, typename FirstType,
          typename... RemainingTypes>
struct GetIndexImpl<T, Counter, FirstType, RemainingTypes...> {
  int static constexpr GetValue() {
    // TODO(lukas) after changing to c++17: change to if constexpr (...)
    if (std::is_same<T, FirstType>::value) {
      return Counter;
    } else {
      return GetIndexImpl<T, Counter + 1, RemainingTypes...>::GetValue();
    }
  }
};
 
}  // namespace detail
 
template <typename TTuple, typename TFunction>
void Apply(TTuple* t, size_t index, TFunction&& f) {
  detail::Apply(t, index, f,
                std::make_index_sequence<std::tuple_size<TTuple>::value>());
}
 
template <typename T, typename... Types>
inline constexpr int GetIndex() {
  return bdm::detail::template GetIndexImpl<T, 0, Types...>::GetValue();
}
 
}  // namespace bdm
 
#endif  // CORE_UTIL_TUPLE_H_