hybridutilities.hh

// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
// vi: set et ts=4 sw=2 sts=2:
#ifndef DUNE_COMMON_HYBRIDUTILITIES_HH
#define DUNE_COMMON_HYBRIDUTILITIES_HH
 
#include <tuple>
#include <utility>
 
#include <dune/common/typeutilities.hh>
#include <dune/common/fvector.hh>
#include <dune/common/indices.hh>
 
 
 
namespace Dune {
namespace Hybrid {
 
namespace Impl {
 
  // Try if tuple_size is implemented for class
  template<class T, int i>
  constexpr auto size(const Dune::FieldVector<T, i>*, const PriorityTag<5>&)
    -> decltype(std::integral_constant<std::size_t,i>())
  {
    return {};
  }
 
  // Try if we have an instance of std::integer_sequence
  template<class T, T... t, class Index>
  constexpr auto size(std::integer_sequence<T, t...>, PriorityTag<4>)
  {
    using sizeAsType = std::tuple_size<decltype(std::make_tuple(t...))>;
    return std::integral_constant<std::size_t, sizeAsType::value>();
  }
 
  // Try if tuple_size is implemented for class
  template<class T>
  constexpr auto size(const T*, const PriorityTag<3>&)
    -> decltype(std::integral_constant<std::size_t,std::tuple_size<T>::value>())
  {
    return {};
  }
 
  // Try if there's a static constexpr size()
  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 static constexpr 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 std::get<std::decay_t<Index>::value>(std::make_tuple(std::integral_constant<T, t>()...));
  }
 
  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>
  class StaticIntegralRange
  {
  public:
 
    template<std::size_t i>
    constexpr auto operator[](Dune::index_constant<i>) const
    {
      return std::integral_constant<typename Begin::value_type, Begin::value+i>();
    }
 
    static constexpr auto size()
    {
      return std::integral_constant<typename Begin::value_type, End::value - Begin::value>();
    }
  };
 
  template<class T>
  class DynamicIntegralRange
  {
  public:
    constexpr DynamicIntegralRange(const T& begin, const T& end):
      begin_(begin),
      end_(end)
    {}
 
    constexpr auto size() const
    {
      return end_ - begin_;
    }
 
    constexpr T operator[](const T&i) const
    { return begin_+i; }
 
  private:
    T begin_;
    T end_;
  };
 
  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 Impl::StaticIntegralRange<Begin,End>();
  }
 
  // This should be constexpr but gcc-4.9 does not support
  // the relaxed constexpr requirements. Hence for beeing
  // constexpr the function body can only contain a return
  // statement and no assertion before this.
  template<class Begin, class End>
  auto integralRange(const Begin& begin, const End& end, const PriorityTag<0>&)
  {
    assert(begin <= end);
    return Impl::DynamicIntegralRange<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>
  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(std::size_t i=0; i<range.size(); ++i)
      f(range[i]);
    // \todo Switch to real range for once DynamicIntegralRange has proper iterators
    //  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>
T accumulate(Range&& range, T value, F&& f)
{
  forEach(std::forward<Range>(range), [&](auto&& entry) {
    value = f(value, entry);
  });
  return value;
}
 
 
 
namespace Impl {
 
  template<class IfFunc, class ElseFunc>
  constexpr decltype(auto) ifElse(std::true_type, IfFunc&& ifFunc, ElseFunc&& elseFunc)
  {
    return ifFunc([](auto&& x) -> decltype(auto) { return std::forward<decltype(x)>(x);});
  }
 
  template<class IfFunc, class ElseFunc>
  constexpr decltype(auto) ifElse(std::false_type, IfFunc&& ifFunc, ElseFunc&& elseFunc)
  {
    return elseFunc([](auto&& x) -> decltype(auto) { return std::forward<decltype(x)>(x);});
  }
 
  template<class IfFunc, class ElseFunc>
  decltype(auto) ifElse(const bool& condition, IfFunc&& ifFunc, ElseFunc&& elseFunc)
  {
    if (condition)
      return ifFunc([](auto&& x) -> decltype(auto) { return std::forward<decltype(x)>(x);});
    else
      return elseFunc([](auto&& x) -> decltype(auto) { return std::forward<decltype(x)>(x);});
  }
 
} // 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&& i) {});
}
 
 
 
namespace Impl {
 
  template<class T1, class T2>
  constexpr auto equals(const T1& t1, const T2& t2, PriorityTag<1>) -> decltype(T1::value, T2::value, std::integral_constant<bool,T1::value == T2::value>())
  { return {}; }
 
  template<class T1, class T2>
  constexpr auto equals(const T1& t1, const T2& t2, PriorityTag<0>)
  {
    return t1==t2;
  }
 
} // namespace Impl
 
 
 
template<class T1, class T2>
constexpr auto equals(T1&& t1,  T2&& t2)
{
  return Impl::equals(std::forward<T1>(t1), std::forward<T2>(t2), PriorityTag<1>());
}
 
 
 
namespace Impl {
 
  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)
  {
    return ifElse(
        Hybrid::equals(std::integral_constant<T, t0>(), value),
      [&](auto id) -> decltype(auto) {
        return id(branches)(std::integral_constant<T, t0>());
      }, [&](auto id) -> decltype(auto) {
        return Impl::switchCases<Result>(id(std::integer_sequence<T, tt...>()), 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)
{
  return Impl::switchCases<void>(cases, value, std::forward<Branches>(branches), []() {});
}
 
 
} // namespace Hybrid
} // namespace Dune
 
 
#endif // #ifndef DUNE_COMMON_HYBRIDUTILITIES_HH