hybridutilities.hh

Go to the documentation of this file.

// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
// vi: set et ts=4 sw=2 sts=2:
// SPDX-FileCopyrightInfo: Copyright © DUNE Project contributors, see file LICENSE.md in module root
// SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
#ifndef DUNE_COMMON_HYBRIDUTILITIES_HH
#define DUNE_COMMON_HYBRIDUTILITIES_HH

#include <tuple>
#include <utility>

#include <dune/common/typetraits.hh>
#include <dune/common/typeutilities.hh>
#include <dune/common/fvector.hh>
#include <dune/common/indices.hh>
#include <dune/common/integersequence.hh>
#include <dune/common/rangeutilities.hh>



namespace Dune {

namespace Hybrid {

namespace Impl {

  // Try if std::tuple_size is implemented for class
  template<class T>
  constexpr auto size(const T&, const PriorityTag<2>&)
    -> decltype(std::integral_constant<std::size_t,std::tuple_size<T>::value>())
  {
    return {};
  }

  // Try if there's a static constexpr size() method
  template<class T>
  constexpr auto size(const T&, const PriorityTag<1>&)
    -> decltype(std::integral_constant<std::size_t,T::size()>())
  {
    return {};
  }

  // As a last resort try if there's a non-static size()
  template<class T>
  constexpr auto size(const T& t, const PriorityTag<0>&)
  {
    return t.size();
  }

} // namespace Impl



template<class T>
constexpr auto size(const T& t)
{
  return Impl::size(t, PriorityTag<42>());
}



namespace Impl {

  template<class Container, class Index,
    std::enable_if_t<IsTuple<std::decay_t<Container>>::value, int> = 0>
  constexpr decltype(auto) elementAt(Container&& c, Index&&, PriorityTag<2>)
  {
    return std::get<std::decay_t<Index>::value>(c);
  }

  template<class T, T... t, class Index>
  constexpr decltype(auto) elementAt(std::integer_sequence<T, t...> c, Index, PriorityTag<1>)
  {
    return Dune::get<Index::value>(c);
  }

  template<class Container, class Index>
  constexpr decltype(auto) elementAt(Container&& c, Index&& i, PriorityTag<0>)
  {
    return c[i];
  }

} // namespace Impl



template<class Container, class Index>
constexpr decltype(auto) elementAt(Container&& c, Index&& i)
{
  return Impl::elementAt(std::forward<Container>(c), std::forward<Index>(i), PriorityTag<42>());
}



namespace Impl {

  template<class Begin, class End,
    std::enable_if_t<IsIntegralConstant<Begin>::value and IsIntegralConstant<End>::value, int> = 0>
  constexpr auto integralRange(const Begin& /*begin*/, const End& /*end*/, const PriorityTag<1>&)
  {
    static_assert(Begin::value <= End::value, "You cannot create an integralRange where end<begin");
    return Dune::StaticIntegralRange<std::size_t, End::value, Begin::value>();
  }

  template<class Begin, class End>
  constexpr auto integralRange(const Begin& begin, const End& end, const PriorityTag<0>&)
  {
    assert(begin<=end && "You cannot create an integralRange where end<begin");
    return Dune::IntegralRange<End>(begin, end);
  }

} // namespace Impl



template<class Begin, class End>
constexpr auto integralRange(const Begin& begin, const End& end)
{
  return Impl::integralRange(begin, end, PriorityTag<42>());
}

template<class End>
constexpr auto integralRange(const End& end)
{
  return Impl::integralRange(Dune::Indices::_0, end, PriorityTag<42>());
}



namespace Impl {

  template<class T>
  constexpr void evaluateFoldExpression(std::initializer_list<T>&&)
  {}

  template<class Range, class F, class Index, Index... i>
  constexpr void forEachIndex(Range&& range, F&& f, std::integer_sequence<Index, i...>)
  {
    evaluateFoldExpression<int>({(f(Hybrid::elementAt(range, std::integral_constant<Index,i>())), 0)...});
  }

  template<class F, class Index, Index... i>
  constexpr void forEach(std::integer_sequence<Index, i...> /*range*/, F&& f, PriorityTag<2>)
  {
    evaluateFoldExpression<int>({(f(std::integral_constant<Index,i>()), 0)...});
  }


  template<class Range, class F,
    std::enable_if_t<IsIntegralConstant<decltype(Hybrid::size(std::declval<Range>()))>::value, int> = 0>
  constexpr void forEach(Range&& range, F&& f, PriorityTag<1>)
  {
    auto size = Hybrid::size(range);
    auto indices = std::make_index_sequence<size>();
    (forEachIndex)(std::forward<Range>(range), std::forward<F>(f), indices);
  }

  template<class Range, class F>
  constexpr void forEach(Range&& range, F&& f, PriorityTag<0>)
  {
      for(auto&& e : range)
        f(e);
  }

} // namespace Impl



template<class Range, class F>
constexpr void forEach(Range&& range, F&& f)
{
  Impl::forEach(std::forward<Range>(range), std::forward<F>(f), PriorityTag<42>());
}



template<class Range, class T, class F>
constexpr T accumulate(Range&& range, T value, F&& f)
{
  forEach(std::forward<Range>(range), [&](auto&& entry) {
    value = f(value, entry);
  });
  return value;
}



namespace Impl {

  struct Id {
    template<class T>
    constexpr T operator()(T&& x) const {
      return std::forward<T>(x);
    }
  };

  template<class IfFunc, class ElseFunc>
  constexpr decltype(auto) ifElse(std::true_type, IfFunc&& ifFunc, ElseFunc&& /*elseFunc*/)
  {
    return ifFunc(Id{});
  }

  template<class IfFunc, class ElseFunc>
  constexpr decltype(auto) ifElse(std::false_type, IfFunc&& /*ifFunc*/, ElseFunc&& elseFunc)
  {
    return elseFunc(Id{});
  }

  template<class IfFunc, class ElseFunc>
  decltype(auto) ifElse(const bool& condition, IfFunc&& ifFunc, ElseFunc&& elseFunc)
  {
    if (condition)
      return ifFunc(Id{});
    else
      return elseFunc(Id{});
  }

} // namespace Impl



template<class Condition, class IfFunc, class ElseFunc>
decltype(auto) ifElse(const Condition& condition, IfFunc&& ifFunc, ElseFunc&& elseFunc)
{
  return Impl::ifElse(condition, std::forward<IfFunc>(ifFunc), std::forward<ElseFunc>(elseFunc));
}

template<class Condition, class IfFunc>
void ifElse(const Condition& condition, IfFunc&& ifFunc)
{
  ifElse(condition, std::forward<IfFunc>(ifFunc), [](auto&&) {});
}



namespace Impl {

  struct Max {
    template<class... Args>
    constexpr decltype(auto) operator()(Args&&... args) const
    {
      using T = std::common_type_t<Args...>;
      return std::max({T(args)...});
    }
  };

  struct Min {
    template<class... Args>
    constexpr decltype(auto) operator()(Args&&... args) const
    {
      using T = std::common_type_t<Args...>;
      return std::min({T(args)...});
    }
  };

} // namespace Impl


template<class Functor>
class HybridFunctor {

  static_assert(std::is_default_constructible_v<Functor>,
    "Operator in integral expressions shall be constexpr default constructible");

  inline static constexpr Functor _functor = Functor{};

public:

  template<class... Args>
  constexpr decltype(auto) operator()(const Args&... args) const
  {
    if constexpr (std::conjunction_v<IsCompileTimeConstant<Args>...>)
    {
      constexpr auto result = _functor(Args::value...);
      // apply functor on integral constant arguments and return an integral constant of the result
      // this is guaranteed to be evaluated at compile-time
      return std::integral_constant<std::remove_cv_t<decltype(result)>,result>{};
    } else {
      // apply functor directly on arguments and return the result of the functor
      // (integral constants are likely to be casted to underlying type)
      // this not is guaranteed to be evaluated at compile-time although is possible if expression is constexpr
      return _functor(args...);
    }
  }
};

template<class Functor>
constexpr HybridFunctor<Functor> hybridFunctor(const Functor&)
{
  return {};
}

inline constexpr auto max = hybridFunctor(Impl::Max{});

inline constexpr auto min = hybridFunctor(Impl::Min{});

inline constexpr auto plus = hybridFunctor(std::plus<>{});

inline constexpr auto minus = hybridFunctor(std::minus<>{});

inline constexpr auto equal_to = hybridFunctor(std::equal_to<>{});


namespace Impl {

  // This overload is selected if the passed value is already a compile time constant.
  template<class Result, class T, T t0, T... tt, class ValueType, ValueType value, class Branches, class ElseBranch>
  constexpr Result switchCases(std::integer_sequence<T, t0, tt...>, const std::integral_constant<ValueType, value>& /*value*/, Branches&& branches, ElseBranch&& elseBranch)
  {
    // In case we pass a value known at compile time, we no longer have to do
    // a dynamic to static dispatch via recursion. The only thing that's left
    // is to check if the value is contained in the passed range.
    // If this is true, we have to pass it to the branches callback
    // as an appropriate integral_constant type. Otherwise we have to
    // execute the else callback.
    if constexpr (((t0 == value) || ... || (tt == value)))
      return branches(std::integral_constant<T, value>{});
    else
      return elseBranch();
  }

  // This overload is selected if the passed value is dynamic.
  template<class Result, class T, class Value, class Branches, class ElseBranch>
  constexpr Result switchCases(std::integer_sequence<T>, const Value& /*value*/, Branches&& /*branches*/, ElseBranch&& elseBranch)
  {
    return elseBranch();
  }

  template<class Result, class T, T t0, T... tt, class Value, class Branches, class ElseBranch>
  constexpr Result switchCases(std::integer_sequence<T, t0, tt...>, const Value& value, Branches&& branches, ElseBranch&& elseBranch)
  {
    if (t0 == value)
      return branches(std::integral_constant<T, t0>());
    else
      return Impl::switchCases<Result>(std::integer_sequence<T, tt...>(), value, branches, elseBranch);
  }

  // This overload is selected if the range of cases is an IntegralRange
  template <class Result, class T, class Value, class Branches, class ElseBranch>
  constexpr Result switchCases(IntegralRange<T> range, const Value& value, Branches&& branches, ElseBranch&& elseBranch)
  {
    return range.contains(value) ? branches(T(value)) : elseBranch();
  }

  // This overload is selected if the range of cases is a StaticIntegralRange
  template <class Result, class T, T to, T from, class Value, class Branches, class ElseBranch>
  constexpr Result switchCases(StaticIntegralRange<T, to, from> range, const Value& value, Branches&& branches, ElseBranch&& elseBranch)
  {
    using seq = typename decltype(range)::integer_sequence;
    return Impl::switchCases<Result>(seq{}, value, branches, elseBranch);
  }

} // namespace Impl



template<class Cases, class Value, class Branches, class ElseBranch>
constexpr decltype(auto) switchCases(const Cases& cases, const Value& value, Branches&& branches, ElseBranch&& elseBranch)
{
  return Impl::switchCases<decltype(elseBranch())>(cases, value, std::forward<Branches>(branches), std::forward<ElseBranch>(elseBranch));
}

template<class Cases, class Value, class Branches>
constexpr void switchCases(const Cases& cases, const Value& value, Branches&& branches)
{
  Impl::switchCases<void>(cases, value, std::forward<Branches>(branches),
    []{ assert(false && "value not found in range"); });
}

template <class T, class Value, class Branches>
constexpr void switchCases(IntegralRange<T> range, const Value& value, Branches&& branches)
{
  assert(range.contains(value) && "value not found in range");
  branches(T(value));
}

} // namespace Hybrid
} // namespace Dune


#endif // #ifndef DUNE_COMMON_HYBRIDUTILITIES_HH