localfiniteelementvariant.hh

// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
// vi: set et ts=4 sw=2 sts=2:
#ifndef DUNE_LOCALFUNCTIONS_COMMON_LOCALFINITEELEMENTVARIANT_HH
#define DUNE_LOCALFUNCTIONS_COMMON_LOCALFINITEELEMENTVARIANT_HH
 
#include <cstddef>
#include <type_traits>
#include <variant>
 
#include <dune/common/typeutilities.hh>
#include <dune/common/std/type_traits.hh>
#include <dune/common/overloadset.hh>
 
#include <dune/geometry/type.hh>
 
#include <dune/localfunctions/common/localfiniteelementtraits.hh>
#include <dune/localfunctions/common/localbasis.hh>
#include <dune/localfunctions/common/localkey.hh>
 
 
namespace Dune {
 
namespace Impl {
 
  // Helper for visiting a variant containing monostate.
  // Since a generic lambda will in most cases not compile
  // for monostate, we add special empty overloads for monostate.
  // Hence visitIf will simply do nothing in the case of a
  // monostate value.
  template<class Visitor, class Variant>
  void visitIf(Visitor&& visitor, Variant&& variant)
  {
    auto visitorWithFallback = overload([&](std::monostate& impl) {},  [&](const std::monostate& impl) {}, visitor);
    std::visit(visitorWithFallback, variant);
  }
 
  template<class... Implementations>
  class LocalBasisVariant
  {
 
    template<class I0, class... II>
    struct FirstType
    { using type = I0; };
 
    using FirstImpTraits = typename FirstType<Implementations...>::type::Traits;
 
  public:
 
    // We do not simply copy Implementation::LocalBasisTraits because this
    // may be implementation specific. To stay clean, we simply put all its
    // data into the default LocalBasisTraits.
    using Traits = typename Dune::LocalBasisTraits<
      typename FirstImpTraits::DomainFieldType,
      FirstImpTraits::dimDomain,
      typename FirstImpTraits::DomainType,
      typename FirstImpTraits::RangeFieldType,
      FirstImpTraits::dimRange,
      typename FirstImpTraits::RangeType,
      typename FirstImpTraits::JacobianType>;
 
    template<class Implementation>
    LocalBasisVariant(const Implementation& impl) :
      impl_(&impl),
      size_(impl.size()),
      order_(impl.order())
    {}
 
    LocalBasisVariant() = default;
    LocalBasisVariant(const LocalBasisVariant& other) = default;
    LocalBasisVariant(LocalBasisVariant&& other) = default;
    LocalBasisVariant& operator=(const LocalBasisVariant& other) = default;
    LocalBasisVariant& operator=(LocalBasisVariant&& other) = default;
 
    unsigned int size() const
    {
      return size_;
    }
 
    unsigned int order() const
    {
      return order_;
    }
 
    inline void evaluateFunction(
        const typename Traits::DomainType& x,
        std::vector<typename Traits::RangeType>& out) const
    {
      Impl::visitIf([&](const auto* impl) { impl->evaluateFunction(x, out); }, impl_);
    }
 
    inline void evaluateJacobian(
        const typename Traits::DomainType& x,
        std::vector<typename Traits::JacobianType>& out) const
    {
      Impl::visitIf([&](const auto* impl) { impl->evaluateJacobian(x, out); }, impl_);
    }
 
    void partial(
        const std::array<unsigned int,Traits::dimDomain>& order,
        const typename Traits::DomainType& x,
        std::vector<typename Traits::RangeType>& out) const
    {
      Impl::visitIf([&](const auto* impl) { impl->partial(order, x, out); }, impl_);
    }
 
  private:
    std::variant<std::monostate, const Implementations*...> impl_;
    std::size_t size_;
    std::size_t order_;
  };
 
 
  template<class... Implementations>
  class LocalCoefficientsVariant
  {
  public:
 
    template<class Implementation>
    LocalCoefficientsVariant(const Implementation& impl) :
      impl_(&impl),
      size_(impl.size())
    {}
 
    LocalCoefficientsVariant() = default;
    LocalCoefficientsVariant(const LocalCoefficientsVariant& other) = default;
    LocalCoefficientsVariant(LocalCoefficientsVariant&& other) = default;
    LocalCoefficientsVariant& operator=(const LocalCoefficientsVariant& other) = default;
    LocalCoefficientsVariant& operator=(LocalCoefficientsVariant&& other) = default;
 
    unsigned int size() const
    {
      return size_;
    }
 
    const Dune::LocalKey& localKey (std::size_t i) const
    {
      // We can't use visitIf since we have to return something
      // even for a monostate value. Since the return type is
      // an l-value reference, we use a default constructed
      // dummy LocalKey value.
      static const Dune::LocalKey dummyLocalKey;
      return std::visit(overload(
          [&](const std::monostate& impl) -> decltype(auto) { return (dummyLocalKey);},
          [&](const auto* impl) -> decltype(auto) { return impl->localKey(i); }), impl_);
    }
 
  private:
    std::variant<std::monostate, const Implementations*...> impl_;
    std::size_t size_;
  };
 
 
  template<class... Implementations>
  class LocalInterpolationVariant
  {
  public:
 
    template<class Implementation>
    LocalInterpolationVariant(const Implementation& impl) :
      impl_(&impl)
    {}
 
    LocalInterpolationVariant() = default;
    LocalInterpolationVariant(const LocalInterpolationVariant& other) = default;
    LocalInterpolationVariant(LocalInterpolationVariant&& other) = default;
    LocalInterpolationVariant& operator=(const LocalInterpolationVariant& other) = default;
    LocalInterpolationVariant& operator=(LocalInterpolationVariant&& other) = default;
 
    template<typename F, typename C>
    void interpolate (const F& ff, std::vector<C>& out) const
    {
      Impl::visitIf([&](const auto* impl) { impl->interpolate(ff, out); }, impl_);
    }
 
  private:
    std::variant<std::monostate, const Implementations*...> impl_;
  };
 
} // namespace Impl
 
 
  template<class... Implementations>
  class LocalFiniteElementVariant
  {
 
    // In each LocalFooVariant we store a std::variant<std::monostate, const FooImpl*...>, i.e. a std::variant
    // with the pointer to the Foo implementation unless LocalFiniteElementVariant stores a monostate. In this
    // case each LocalFooVariant also stores a monostate (and not a monostate*).
    using LocalBasis = Impl::LocalBasisVariant<typename Implementations::Traits::LocalBasisType...>;
    using LocalCoefficients = Impl::LocalCoefficientsVariant<typename Implementations::Traits::LocalCoefficientsType...>;
    using LocalInterpolation = Impl::LocalInterpolationVariant<typename Implementations::Traits::LocalInterpolationType...>;
 
    // Update members after changing impl_
    void updateMembers()
    {
      std::visit(overload(
          [&](std::monostate&) {
            localBasis_ = LocalBasis();
            localCoefficients_ = LocalCoefficients();
            localInterpolation_ = LocalInterpolation();
            size_ = 0;
            geometryType_ = GeometryType{};
          }, [&](auto&& impl) {
            localBasis_ = LocalBasis(impl.localBasis());
            localCoefficients_ = LocalCoefficients(impl.localCoefficients());
            localInterpolation_ = LocalInterpolation(impl.localInterpolation());
            size_ = impl.size();
            geometryType_ = impl.type();
          }), impl_);
    }
 
  public:
 
    using Traits = typename Dune::LocalFiniteElementTraits<LocalBasis, LocalCoefficients, LocalInterpolation>;
 
    LocalFiniteElementVariant() = default;
 
    LocalFiniteElementVariant(const std::monostate& monostate)
    {}
 
    template<class Implementation,
      std::enable_if_t<std::disjunction<std::is_same<std::decay_t<Implementation>, Implementations>...>::value, int> = 0>
    LocalFiniteElementVariant(Implementation&& impl) :
      impl_(std::forward<Implementation>(impl))
    {
      updateMembers();
    }
 
    LocalFiniteElementVariant(const LocalFiniteElementVariant& other) :
      impl_(other.impl_)
    {
      updateMembers();
    }
 
    LocalFiniteElementVariant(LocalFiniteElementVariant&& other) :
      impl_(std::move(other.impl_))
    {
      updateMembers();
    }
 
    LocalFiniteElementVariant& operator=(const LocalFiniteElementVariant& other)
    {
      impl_ = other.impl_;
      updateMembers();
      return *this;
    }
 
    LocalFiniteElementVariant& operator=(LocalFiniteElementVariant&& other)
    {
      impl_ = std::move(other.impl_);
      updateMembers();
      return *this;
    }
 
    template<class Implementation,
      std::enable_if_t<std::disjunction<std::is_same<std::decay_t<Implementation>, Implementations>...>::value, int> = 0>
    LocalFiniteElementVariant& operator=(Implementation&& impl)
    {
      impl_ = std::forward<Implementation>(impl);
      updateMembers();
      return *this;
    }
 
 
    const typename Traits::LocalBasisType& localBasis() const
    {
      return localBasis_;
    }
 
    const typename Traits::LocalCoefficientsType& localCoefficients() const
    {
      return localCoefficients_;
    }
 
    const typename Traits::LocalInterpolationType& localInterpolation() const
    {
      return localInterpolation_;
    }
 
    unsigned int size() const
    {
      return size_;
    }
 
    constexpr GeometryType type() const
    {
      return geometryType_;
    }
 
    const auto& variant() const
    {
      return impl_;
    }
 
    operator bool () const
    {
      return not(std::holds_alternative<std::monostate>(variant()));
    }
 
  private:
    std::variant<std::monostate, Implementations...> impl_;
    std::size_t size_;
    GeometryType geometryType_;
    LocalBasis localBasis_;
    LocalCoefficients localCoefficients_;
    LocalInterpolation localInterpolation_;
  };
 
} // end namespace Dune
 
#endif // DUNE_LOCALFUNCTIONS_COMMON_LOCALFINITEELEMENTVARIANT_HH