istlvectorbackend.hh

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// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
// vi: set et ts=4 sw=2 sts=2:
 
// SPDX-FileCopyrightText: Copyright © DUNE Project contributors, see file AUTHORS.md
// SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception OR LGPL-3.0-or-later
 
#ifndef DUNE_FUNCTIONS_FUNCTIONSPACEBASES_ISTLVECTORBACKEND_HH
#define DUNE_FUNCTIONS_FUNCTIONSPACEBASES_ISTLVECTORBACKEND_HH
 
#include <cstddef>
#include <utility>
#include <type_traits>
 
#include <dune/common/std/type_traits.hh>
#include <dune/common/indices.hh>
#include <dune/common/hybridutilities.hh>
#include <dune/common/concept.hh>
 
#include <dune/functions/common/indexaccess.hh>
#include <dune/functions/functionspacebases/concepts.hh>
 
 
namespace Dune {
namespace Functions {
 
namespace Impl {
 
template<class V,
  std::enable_if_t<not Dune::models<Imp::Concept::HasStaticIndexAccess, V>() , int> = 0>
auto fieldTypes(V&& /*v*/)
{
  return TypeList<V>{};
}
 
template<class V,
  std::enable_if_t<Dune::models<Imp::Concept::HasStaticIndexAccess, V>(), int> = 0>
auto fieldTypes(V&& v)
{
  if constexpr (Dune::models<Imp::Concept::HasDynamicIndexAccess<std::size_t>, V>())
     return fieldTypes(v[std::size_t{0}]);
  else
  {
    auto indexRange = typename decltype(range(Hybrid::size(v)))::integer_sequence();
    return unpackIntegerSequence([&](auto... i) {
      return uniqueTypeList(std::tuple_cat(fieldTypes(v[i])...));
    }, indexRange);
  }
}
 
} // namespace Impl
 
 
 
template<class V>
constexpr auto fieldTypes()
{
  return decltype(Impl::fieldTypes(std::declval<V>())){};
}
 
template<class V>
constexpr bool hasUniqueFieldType()
{
  return std::tuple_size_v<std::decay_t<decltype(fieldTypes<V>())>> ==1;
}
 
 
 
namespace Impl {
 
/*
 * \brief A wrapper providing multi-index access to vector entries
 *
 * The wrapped vector type should be an istl like random
 * access container providing operator[] and size() methods.
 * For classical containers this should support indices
 * of type std::size_t. For multi-type containers indices
 * of the form Dune::index_constant<i> should be supported
 * while size() should be a static constexpr method.
 *
 * When resolving multi-indices the backend appends indices
 * using operator[] as long as the result is not a scalar.
 * If this exhausts the digits of the multi-index, additional
 * zeros are appended.
 *
 * \tparam V Type of the raw wrapper vector
 */
template<class V>
class ISTLVectorBackend
{
 
  // Template aliases for using detection idiom.
  template<class C>
  using dynamicIndexAccess_t = decltype(std::declval<C>()[0]);
 
  template<class C>
  using staticIndexAccess_t = decltype(std::declval<C>()[Dune::Indices::_0]);
 
  template<class C>
  using resizeMethod_t = decltype(std::declval<C>().resize(0));
 
 
 
  // Short cuts for feature detection
  template<class C>
  using hasDynamicIndexAccess = Dune::Std::is_detected<dynamicIndexAccess_t, std::remove_reference_t<C>>;
 
  template<class C>
  using hasStaticIndexAccess = Dune::Std::is_detected<staticIndexAccess_t, std::remove_reference_t<C>>;
 
  template<class C>
  using hasResizeMethod = Dune::Std::is_detected<resizeMethod_t, std::remove_reference_t<C>>;
 
  template<class C>
  using isDynamicVector = Dune::Std::is_detected<dynamicIndexAccess_t, std::remove_reference_t<C>>;
 
  template<class C>
  using isStaticVector = std::bool_constant<
    Dune::Std::is_detected_v<staticIndexAccess_t, std::remove_reference_t<C>>
    and not Dune::Std::is_detected_v<dynamicIndexAccess_t, std::remove_reference_t<C>>>;
 
  template<class C>
  using isScalar = std::bool_constant<(not Dune::Std::is_detected_v<staticIndexAccess_t, std::remove_reference_t<C>>) or Dune::IsNumber<C>::value>;
 
  template<class C>
  using isVector = std::bool_constant<Dune::Std::is_detected_v<staticIndexAccess_t, std::remove_reference_t<C>>>;
 
 
 
  template<class... Args>
  static void forwardToResize(Args&&... args)
  {
    resize(std::forward<Args>(args)...);
  }
 
 
  template<class C, class SizeProvider,
    std::enable_if_t<hasResizeMethod<C>::value, int> = 0>
  static void resize(C&& c, const SizeProvider& sizeProvider, typename SizeProvider::SizePrefix prefix)
  {
    auto size = sizeProvider.size(prefix);
    if (size==0)
    {
      // If size==0 this prefix refers to a single coefficient c.
      // But being in this overload means that c is not a scalar
      // because is has a resize() method. Since operator[] deliberately
      // supports implicit padding of multi-indices by as many
      // [0]'s as needed to resolve a scalar entry, we should also
      // except a non-scalar c here. However, this requires that
      // we silently believe that whatever size c already has is
      // intended by the user. The only exception is c.size()==0
      // which is not acceptable but we also cannot know the desired size.
      if (c.size()==0)
        DUNE_THROW(RangeError, "The vector entry v[" << prefix << "] should refer to a "
                                << "scalar coefficient, but is a dynamically sized vector of size==0");
      else
        // Accept non-zero sized coefficients to avoid that resize(basis)
        // fails for a vector that works with operator[] and already
        // has the appropriate size.
        return;
    }
    c.resize(size);
    prefix.push_back(0);
    for(std::size_t i=0; i<size; ++i)
    {
      prefix.back() = i;
      resize(c[i], sizeProvider, prefix);
    }
  }
 
  template<class C, class SizeProvider,
    std::enable_if_t<not hasResizeMethod<C>::value, int> = 0,
    std::enable_if_t<isVector<C>::value, int> = 0>
  static void resize(C&& c, const SizeProvider& sizeProvider, typename SizeProvider::SizePrefix prefix)
  {
    auto size = sizeProvider.size(prefix);
    // If size == 0 there's nothing to do:
    // We can't resize c and it's already
    // large enough anyway.
    if (size == 0)
      return;
 
    // If size>0 but c does not have the appropriate
    // size we throw an exception.
    //
    // We could perhaps also allow c.size()>size.
    // But then looping the loop below gets complicated:
    // We're not allowed to loop until c.size(). But
    // we also cannot use size for termination,
    // because this fails if c is a static vector.
    if (c.size() != size)
      DUNE_THROW(RangeError, "Can't resize non-resizable entry v[" << prefix << "] of size " << c.size() << " to size(" << prefix << ")=" << size);
 
    // Recursively resize all entries of c now.
    using namespace Dune::Hybrid;
    prefix.push_back(0);
    forEach(integralRange(Hybrid::size(c)), [&](auto&& i) {
      prefix.back() = i;
      // Here we'd simply like to call resize(c[i], sizeProvider, prefix);
      // but even gcc-7 does not except this bus reports
      // "error: ‘this’ was not captured for this lambda function"
      // although there's no 'this' because we're in a static method.
      // Bypassing this by and additional method that does perfect
      // forwarding allows to workaround this.
      ISTLVectorBackend<V>::forwardToResize(c[i], sizeProvider, prefix);
    });
  }
 
  template<class C, class SizeProvider,
    std::enable_if_t<not hasResizeMethod<C>::value, int> = 0,
    std::enable_if_t<isScalar<C>::value, int> = 0>
  static void resize(C&&, const SizeProvider& sizeProvider, typename SizeProvider::SizePrefix prefix)
  {
    auto size = sizeProvider.size(prefix);
    if (size != 0)
      DUNE_THROW(RangeError, "Can't resize scalar vector entry v[" << prefix << "] to size(" << prefix << ")=" << size);
  }
 
  template<class C, class T,
    std::enable_if_t<std::is_assignable_v<C&,T>, int> = 0>
  void recursiveAssign(C& c, const T& t)
  {
    c = t;
  }
 
  template<class C, class T,
    std::enable_if_t<not std::is_assignable_v<C&,T>, int> = 0>
  void recursiveAssign(C& c, const T& t)
  {
    Dune::Hybrid::forEach(c, [&](auto&& ci) {
      recursiveAssign(ci, t);
    });
  }
 
public:
 
  using Vector = V;
 
  ISTLVectorBackend(Vector& vector) :
    vector_(&vector)
  {}
 
  template<class SizeProvider>
  void resize(const SizeProvider& sizeProvider)
  {
    auto prefix = typename SizeProvider::SizePrefix();
    prefix.resize(0);
    resize(*vector_, sizeProvider, prefix);
  }
 
  template<class MultiIndex>
  decltype(auto) operator[](const MultiIndex& index) const
  {
    auto termination = [](auto&& c) { return isScalar<std::decay_t<decltype(c)>>{}; };
    return resolveDynamicMultiIndex(*vector_, index, termination);
  }
 
  template<class MultiIndex>
  decltype(auto) operator[](const MultiIndex& index)
  {
    auto termination = [](auto&& c) { return isScalar<std::decay_t<decltype(c)>>{}; };
    return resolveDynamicMultiIndex(*vector_, index, termination);
  }
 
  template<typename T>
  void operator= (const T& other)
  {
    recursiveAssign(vector(), other);
  }
 
  template<typename T>
  void operator= (const ISTLVectorBackend<T>& other)
  {
    vector() = other.vector();
  }
 
  const Vector& vector() const
  {
    return *vector_;
  }
 
  Vector& vector()
  {
    return *vector_;
  }
 
private:
 
  Vector* vector_;
};
 
} // end namespace Impl
 
 
 
template<class Vector>
auto istlVectorBackend(Vector& v)
{
  static_assert(hasUniqueFieldType<Vector&>(), "Vector type passed to istlVectorBackend() does not have a unique field type.");
  return Impl::ISTLVectorBackend<Vector>(v);
}
 
 
 
template<class Vector>
auto istlVectorBackend(const Vector& v)
{
  static_assert(hasUniqueFieldType<const Vector&>(), "Vector type passed to istlVectorBackend() does not have a unique field type.");
  return Impl::ISTLVectorBackend<const Vector>(v);
}
 
 
 
} // namespace Functions
} // namespace Dune
 
 
#endif // DUNE_FUNCTIONS_FUNCTIONSPACEBASES_ISTLVECTORBACKEND_HH