BLI_virtual_array.hh

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/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */
 
#pragma once
 
#include <optional>
 
#include "BLI_any.hh"
#include "BLI_array.hh"
#include "BLI_devirtualize_parameters.hh"
#include "BLI_index_mask.hh"
#include "BLI_span.hh"
 
namespace blender {
 
class GVArray;
class GVMutableArray;
 
struct CommonVArrayInfo {
  enum class Type : uint8_t {
    /* Is not one of the common special types below. */
    Any,
    Span,
    Single,
  };
 
  Type type = Type::Any;
 
  bool may_have_ownership = true;
 
  const void *data;
 
  CommonVArrayInfo() = default;
  CommonVArrayInfo(const Type _type, const bool _may_have_ownership, const void *_data)
      : type(_type), may_have_ownership(_may_have_ownership), data(_data)
  {
  }
};
 
template<typename T> class VArrayImpl {
 protected:
  int64_t size_;
 
 public:
  VArrayImpl(const int64_t size) : size_(size)
  {
    BLI_assert(size_ >= 0);
  }
 
  virtual ~VArrayImpl() = default;
 
  int64_t size() const
  {
    return size_;
  }
 
  virtual T get(int64_t index) const = 0;
 
  virtual CommonVArrayInfo common_info() const
  {
    return {};
  }
 
  virtual void materialize(const IndexMask &mask, T *dst) const
  {
    mask.foreach_index([&](const int64_t i) { dst[i] = this->get(i); });
  }
 
  virtual void materialize_to_uninitialized(const IndexMask &mask, T *dst) const
  {
    mask.foreach_index([&](const int64_t i) { new (dst + i) T(this->get(i)); });
  }
 
  virtual void materialize_compressed(const IndexMask &mask, T *dst) const
  {
    mask.foreach_index([&](const int64_t i, const int64_t pos) { dst[pos] = this->get(i); });
  }
 
  virtual void materialize_compressed_to_uninitialized(const IndexMask &mask, T *dst) const
  {
    mask.foreach_index(
        [&](const int64_t i, const int64_t pos) { new (dst + pos) T(this->get(i)); });
  }
 
  virtual bool try_assign_GVArray(GVArray & /*varray*/) const
  {
    return false;
  }
};
 
template<typename T> class VMutableArrayImpl : public VArrayImpl<T> {
 public:
  using VArrayImpl<T>::VArrayImpl;
 
  virtual void set(int64_t index, T value) = 0;
 
  virtual void set_all(Span<T> src)
  {
    const CommonVArrayInfo info = this->common_info();
    if (info.type == CommonVArrayInfo::Type::Span) {
      initialized_copy_n(
          src.data(), this->size_, const_cast<T *>(static_cast<const T *>(info.data)));
    }
    else {
      const int64_t size = this->size_;
      for (int64_t i = 0; i < size; i++) {
        this->set(i, src[i]);
      }
    }
  }
 
  virtual bool try_assign_GVMutableArray(GVMutableArray & /*varray*/) const
  {
    return false;
  }
};
 
template<typename T> class VArrayImpl_For_Span : public VMutableArrayImpl<T> {
 protected:
  T *data_ = nullptr;
 
 public:
  VArrayImpl_For_Span(const MutableSpan<T> data)
      : VMutableArrayImpl<T>(data.size()), data_(data.data())
  {
  }
 
 protected:
  VArrayImpl_For_Span(const int64_t size) : VMutableArrayImpl<T>(size) {}
 
  T get(const int64_t index) const final
  {
    return data_[index];
  }
 
  void set(const int64_t index, T value) final
  {
    data_[index] = value;
  }
 
  CommonVArrayInfo common_info() const override
  {
    return CommonVArrayInfo(CommonVArrayInfo::Type::Span, true, data_);
  }
 
  void materialize(const IndexMask &mask, T *dst) const override
  {
    mask.foreach_index_optimized<int64_t>([&](const int64_t i) { dst[i] = data_[i]; });
  }
 
  void materialize_to_uninitialized(const IndexMask &mask, T *dst) const override
  {
    mask.foreach_index_optimized<int64_t>([&](const int64_t i) { new (dst + i) T(data_[i]); });
  }
 
  void materialize_compressed(const IndexMask &mask, T *dst) const override
  {
    mask.foreach_index_optimized<int64_t>(
        [&](const int64_t i, const int64_t pos) { dst[pos] = data_[i]; });
  }
 
  void materialize_compressed_to_uninitialized(const IndexMask &mask, T *dst) const override
  {
    mask.foreach_index_optimized<int64_t>(
        [&](const int64_t i, const int64_t pos) { new (dst + pos) T(data_[i]); });
  }
};
 
template<typename T> class VArrayImpl_For_Span_final final : public VArrayImpl_For_Span<T> {
 public:
  using VArrayImpl_For_Span<T>::VArrayImpl_For_Span;
 
  VArrayImpl_For_Span_final(const Span<T> data)
      /* Cast const away, because the implementation for const and non const spans is shared. */
      : VArrayImpl_For_Span<T>({const_cast<T *>(data.data()), data.size()})
  {
  }
 
 private:
  CommonVArrayInfo common_info() const final
  {
    return CommonVArrayInfo(CommonVArrayInfo::Type::Span, false, this->data_);
  }
};
 
template<typename T>
inline constexpr bool is_trivial_extended_v<VArrayImpl_For_Span_final<T>> = true;
 
template<typename Container, typename T = typename Container::value_type>
class VArrayImpl_For_ArrayContainer : public VArrayImpl_For_Span<T> {
 private:
  Container container_;
 
 public:
  VArrayImpl_For_ArrayContainer(Container container)
      : VArrayImpl_For_Span<T>(int64_t(container.size())), container_(std::move(container))
  {
    this->data_ = const_cast<T *>(container_.data());
  }
};
 
template<typename T> class VArrayImpl_For_Single final : public VArrayImpl<T> {
 private:
  T value_;
 
 public:
  VArrayImpl_For_Single(T value, const int64_t size)
      : VArrayImpl<T>(size), value_(std::move(value))
  {
  }
 
 protected:
  T get(const int64_t /*index*/) const override
  {
    return value_;
  }
 
  CommonVArrayInfo common_info() const override
  {
    return CommonVArrayInfo(CommonVArrayInfo::Type::Single, true, &value_);
  }
 
  void materialize(const IndexMask &mask, T *dst) const override
  {
    mask.foreach_index([&](const int64_t i) { dst[i] = value_; });
  }
 
  void materialize_to_uninitialized(const IndexMask &mask, T *dst) const override
  {
    mask.foreach_index([&](const int64_t i) { new (dst + i) T(value_); });
  }
 
  void materialize_compressed(const IndexMask &mask, T *dst) const override
  {
    initialized_fill_n(dst, mask.size(), value_);
  }
 
  void materialize_compressed_to_uninitialized(const IndexMask &mask, T *dst) const override
  {
    uninitialized_fill_n(dst, mask.size(), value_);
  }
};
 
template<typename T>
inline constexpr bool is_trivial_extended_v<VArrayImpl_For_Single<T>> = is_trivial_extended_v<T>;
 
template<typename T, typename GetFunc> class VArrayImpl_For_Func final : public VArrayImpl<T> {
 private:
  GetFunc get_func_;
 
 public:
  VArrayImpl_For_Func(const int64_t size, GetFunc get_func)
      : VArrayImpl<T>(size), get_func_(std::move(get_func))
  {
  }
 
 private:
  T get(const int64_t index) const override
  {
    return get_func_(index);
  }
 
  void materialize(const IndexMask &mask, T *dst) const override
  {
    mask.foreach_index([&](const int64_t i) { dst[i] = get_func_(i); });
  }
 
  void materialize_to_uninitialized(const IndexMask &mask, T *dst) const override
  {
    mask.foreach_index([&](const int64_t i) { new (dst + i) T(get_func_(i)); });
  }
 
  void materialize_compressed(const IndexMask &mask, T *dst) const override
  {
    mask.foreach_index([&](const int64_t i, const int64_t pos) { dst[pos] = get_func_(i); });
  }
 
  void materialize_compressed_to_uninitialized(const IndexMask &mask, T *dst) const override
  {
    mask.foreach_index(
        [&](const int64_t i, const int64_t pos) { new (dst + pos) T(get_func_(i)); });
  }
};
 
template<typename StructT,
         typename ElemT,
         ElemT (*GetFunc)(const StructT &),
         void (*SetFunc)(StructT &, ElemT) = nullptr>
class VArrayImpl_For_DerivedSpan final : public VMutableArrayImpl<ElemT> {
 private:
  StructT *data_;
 
 public:
  VArrayImpl_For_DerivedSpan(const MutableSpan<StructT> data)
      : VMutableArrayImpl<ElemT>(data.size()), data_(data.data())
  {
  }
 
  template<typename OtherStructT,
           typename OtherElemT,
           OtherElemT (*OtherGetFunc)(const OtherStructT &),
           void (*OtherSetFunc)(OtherStructT &, OtherElemT)>
  friend class VArrayImpl_For_DerivedSpan;
 
 private:
  ElemT get(const int64_t index) const override
  {
    return GetFunc(data_[index]);
  }
 
  void set(const int64_t index, ElemT value) override
  {
    SetFunc(data_[index], std::move(value));
  }
 
  void materialize(const IndexMask &mask, ElemT *dst) const override
  {
    mask.foreach_index_optimized<int64_t>([&](const int64_t i) { dst[i] = GetFunc(data_[i]); });
  }
 
  void materialize_to_uninitialized(const IndexMask &mask, ElemT *dst) const override
  {
    mask.foreach_index_optimized<int64_t>(
        [&](const int64_t i) { new (dst + i) ElemT(GetFunc(data_[i])); });
  }
 
  void materialize_compressed(const IndexMask &mask, ElemT *dst) const override
  {
    mask.foreach_index_optimized<int64_t>(
        [&](const int64_t i, const int64_t pos) { dst[pos] = GetFunc(data_[i]); });
  }
 
  void materialize_compressed_to_uninitialized(const IndexMask &mask, ElemT *dst) const override
  {
    mask.foreach_index_optimized<int64_t>(
        [&](const int64_t i, const int64_t pos) { new (dst + pos) ElemT(GetFunc(data_[i])); });
  }
};
 
template<typename StructT,
         typename ElemT,
         ElemT (*GetFunc)(const StructT &),
         void (*SetFunc)(StructT &, ElemT)>
inline constexpr bool
    is_trivial_extended_v<VArrayImpl_For_DerivedSpan<StructT, ElemT, GetFunc, SetFunc>> = true;
 
namespace detail {
 
template<typename T> struct VArrayAnyExtraInfo {
  const VArrayImpl<T> *(*get_varray)(const void *buffer);
 
  template<typename StorageT> static constexpr VArrayAnyExtraInfo get()
  {
    /* These are the only allowed types in the #Any. */
    static_assert(
        std::is_base_of_v<VArrayImpl<T>, StorageT> ||
        is_same_any_v<StorageT, const VArrayImpl<T> *, std::shared_ptr<const VArrayImpl<T>>>);
 
    /* Depending on how the virtual array implementation is stored in the #Any, a different
     * #get_varray function is required. */
    if constexpr (std::is_base_of_v<VArrayImpl<T>, StorageT>) {
      return {[](const void *buffer) {
        return static_cast<const VArrayImpl<T> *>((const StorageT *)buffer);
      }};
    }
    else if constexpr (std::is_same_v<StorageT, const VArrayImpl<T> *>) {
      return {[](const void *buffer) { return *(const StorageT *)buffer; }};
    }
    else if constexpr (std::is_same_v<StorageT, std::shared_ptr<const VArrayImpl<T>>>) {
      return {[](const void *buffer) { return ((const StorageT *)buffer)->get(); }};
    }
    else {
      BLI_assert_unreachable();
      return {};
    }
  }
};
 
}  // namespace detail
 
template<typename T> class VArrayCommon {
 protected:
  using Storage = Any<blender::detail::VArrayAnyExtraInfo<T>, 24, 8>;
 
  const VArrayImpl<T> *impl_ = nullptr;
  Storage storage_;
 
 protected:
  VArrayCommon() = default;
 
  VArrayCommon(const VArrayCommon &other) : storage_(other.storage_)
  {
    impl_ = this->impl_from_storage();
  }
 
  VArrayCommon(VArrayCommon &&other) noexcept : storage_(std::move(other.storage_))
  {
    impl_ = this->impl_from_storage();
    other.storage_.reset();
    other.impl_ = nullptr;
  }
 
  VArrayCommon(const VArrayImpl<T> *impl) : impl_(impl)
  {
    storage_ = impl_;
  }
 
  VArrayCommon(std::shared_ptr<const VArrayImpl<T>> impl) : impl_(impl.get())
  {
    if (impl) {
      storage_ = std::move(impl);
    }
  }
 
  template<typename ImplT, typename... Args> void emplace(Args &&...args)
  {
    /* Make sure we are actually constructing a #VArrayImpl. */
    static_assert(std::is_base_of_v<VArrayImpl<T>, ImplT>);
    if constexpr (std::is_copy_constructible_v<ImplT> && Storage::template is_inline_v<ImplT>) {
      /* Only inline the implementation when it is copyable and when it fits into the inline
       * buffer of the storage. */
      impl_ = &storage_.template emplace<ImplT>(std::forward<Args>(args)...);
    }
    else {
      /* If it can't be inlined, create a new #std::shared_ptr instead and store that in the
       * storage. */
      std::shared_ptr<const VArrayImpl<T>> ptr = std::make_shared<ImplT>(
          std::forward<Args>(args)...);
      impl_ = &*ptr;
      storage_ = std::move(ptr);
    }
  }
 
  void copy_from(const VArrayCommon &other)
  {
    if (this == &other) {
      return;
    }
    storage_ = other.storage_;
    impl_ = this->impl_from_storage();
  }
 
  void move_from(VArrayCommon &&other) noexcept
  {
    if (this == &other) {
      return;
    }
    storage_ = std::move(other.storage_);
    impl_ = this->impl_from_storage();
    other.storage_.reset();
    other.impl_ = nullptr;
  }
 
  const VArrayImpl<T> *impl_from_storage() const
  {
    if (!storage_.has_value()) {
      return nullptr;
    }
    return storage_.extra_info().get_varray(storage_.get());
  }
 
 public:
  operator bool() const
  {
    return impl_ != nullptr;
  }
 
  T operator[](const int64_t index) const
  {
    BLI_assert(*this);
    BLI_assert(index >= 0);
    BLI_assert(index < this->size());
    return impl_->get(index);
  }
 
  T get(const int64_t index) const
  {
    return (*this)[index];
  }
 
  int64_t size() const
  {
    if (impl_ == nullptr) {
      return 0;
    }
    return impl_->size();
  }
  T first() const
  {
    return (*this)[0];
  }
  T last(const int64_t n = 0) const
  {
    return (*this)[this->size() - 1 - n];
  }
 
  bool is_empty() const
  {
    return this->size() == 0;
  }
 
  IndexRange index_range() const
  {
    return IndexRange(this->size());
  }
 
  CommonVArrayInfo common_info() const
  {
    BLI_assert(*this);
    return impl_->common_info();
  }
 
  bool is_span() const
  {
    BLI_assert(*this);
    const CommonVArrayInfo info = impl_->common_info();
    return info.type == CommonVArrayInfo::Type::Span;
  }
 
  Span<T> get_internal_span() const
  {
    BLI_assert(this->is_span());
    const CommonVArrayInfo info = impl_->common_info();
    return Span<T>(static_cast<const T *>(info.data), this->size());
  }
 
  bool is_single() const
  {
    BLI_assert(*this);
    const CommonVArrayInfo info = impl_->common_info();
    return info.type == CommonVArrayInfo::Type::Single;
  }
 
  T get_internal_single() const
  {
    BLI_assert(this->is_single());
    const CommonVArrayInfo info = impl_->common_info();
    return *static_cast<const T *>(info.data);
  }
 
  std::optional<T> get_if_single() const
  {
    const CommonVArrayInfo info = impl_->common_info();
    if (info.type != CommonVArrayInfo::Type::Single) {
      return std::nullopt;
    }
    return *static_cast<const T *>(info.data);
  }
 
  void materialize(MutableSpan<T> r_span) const
  {
    this->materialize(IndexMask(this->size()), r_span);
  }
 
  void materialize(const IndexMask &mask, MutableSpan<T> r_span) const
  {
    BLI_assert(mask.min_array_size() <= this->size());
    impl_->materialize(mask, r_span.data());
  }
 
  void materialize_to_uninitialized(MutableSpan<T> r_span) const
  {
    this->materialize_to_uninitialized(IndexMask(this->size()), r_span);
  }
 
  void materialize_to_uninitialized(const IndexMask &mask, MutableSpan<T> r_span) const
  {
    BLI_assert(mask.min_array_size() <= this->size());
    impl_->materialize_to_uninitialized(mask, r_span.data());
  }
 
  void materialize_compressed(const IndexMask &mask, MutableSpan<T> r_span) const
  {
    impl_->materialize_compressed(mask, r_span.data());
  }
 
  void materialize_compressed_to_uninitialized(const IndexMask &mask, MutableSpan<T> r_span) const
  {
    impl_->materialize_compressed_to_uninitialized(mask, r_span.data());
  }
 
  bool try_assign_GVArray(GVArray &varray) const
  {
    return impl_->try_assign_GVArray(varray);
  }
 
  const VArrayImpl<T> *get_implementation() const
  {
    return impl_;
  }
};
 
template<typename T> class VMutableArray;
 
namespace varray_tag {
struct span {};
struct single_ref {};
struct single {};
}  // namespace varray_tag
 
template<typename T> class VArray : public VArrayCommon<T> {
  friend VMutableArray<T>;
 
 public:
  VArray() = default;
  VArray(const VArray &other) = default;
  VArray(VArray &&other) noexcept = default;
 
  VArray(const VArrayImpl<T> *impl) : VArrayCommon<T>(impl) {}
 
  VArray(std::shared_ptr<const VArrayImpl<T>> impl) : VArrayCommon<T>(std::move(impl)) {}
 
  VArray(varray_tag::span /*tag*/, Span<T> span)
  {
    this->template emplace<VArrayImpl_For_Span_final<T>>(span);
  }
 
  VArray(varray_tag::single /*tag*/, T value, const int64_t size)
  {
    this->template emplace<VArrayImpl_For_Single<T>>(std::move(value), size);
  }
 
  template<typename ImplT, typename... Args> static VArray For(Args &&...args)
  {
    static_assert(std::is_base_of_v<VArrayImpl<T>, ImplT>);
    VArray varray;
    varray.template emplace<ImplT>(std::forward<Args>(args)...);
    return varray;
  }
 
  static VArray ForSingle(T value, const int64_t size)
  {
    return VArray(varray_tag::single{}, std::move(value), size);
  }
 
  static VArray ForSpan(Span<T> values)
  {
    return VArray(varray_tag::span{}, values);
  }
 
  template<typename GetFunc> static VArray ForFunc(const int64_t size, GetFunc get_func)
  {
    return VArray::For<VArrayImpl_For_Func<T, decltype(get_func)>>(size, std::move(get_func));
  }
 
  template<typename StructT, T (*GetFunc)(const StructT &)>
  static VArray ForDerivedSpan(Span<StructT> values)
  {
    /* Cast const away, because the virtual array implementation for const and non const derived
     * spans is shared. */
    MutableSpan<StructT> span{const_cast<StructT *>(values.data()), values.size()};
    return VArray::For<VArrayImpl_For_DerivedSpan<StructT, T, GetFunc>>(span);
  }
 
  template<typename ContainerT> static VArray ForContainer(ContainerT container)
  {
    return VArray::For<VArrayImpl_For_ArrayContainer<ContainerT>>(std::move(container));
  }
 
  VArray &operator=(const VArray &other)
  {
    this->copy_from(other);
    return *this;
  }
 
  VArray &operator=(VArray &&other) noexcept
  {
    this->move_from(std::move(other));
    return *this;
  }
};
 
template<typename T> class VMutableArray : public VArrayCommon<T> {
 public:
  VMutableArray() = default;
  VMutableArray(const VMutableArray &other) = default;
  VMutableArray(VMutableArray &&other) noexcept = default;
 
  VMutableArray(const VMutableArrayImpl<T> *impl) : VArrayCommon<T>(impl) {}
 
  VMutableArray(std::shared_ptr<const VMutableArrayImpl<T>> impl)
      : VArrayCommon<T>(std::move(impl))
  {
  }
 
  template<typename ImplT, typename... Args> static VMutableArray For(Args &&...args)
  {
    static_assert(std::is_base_of_v<VMutableArrayImpl<T>, ImplT>);
    VMutableArray varray;
    varray.template emplace<ImplT>(std::forward<Args>(args)...);
    return varray;
  }
 
  static VMutableArray ForSpan(MutableSpan<T> values)
  {
    return VMutableArray::For<VArrayImpl_For_Span_final<T>>(values);
  }
 
  template<typename StructT, T (*GetFunc)(const StructT &), void (*SetFunc)(StructT &, T)>
  static VMutableArray ForDerivedSpan(MutableSpan<StructT> values)
  {
    return VMutableArray::For<VArrayImpl_For_DerivedSpan<StructT, T, GetFunc, SetFunc>>(values);
  }
 
  operator VArray<T>() const &
  {
    VArray<T> varray;
    varray.copy_from(*this);
    return varray;
  }
 
  operator VArray<T>() && noexcept
  {
    VArray<T> varray;
    varray.move_from(std::move(*this));
    return varray;
  }
 
  VMutableArray &operator=(const VMutableArray &other)
  {
    this->copy_from(other);
    return *this;
  }
 
  VMutableArray &operator=(VMutableArray &&other) noexcept
  {
    this->move_from(std::move(other));
    return *this;
  }
 
  MutableSpan<T> get_internal_span() const
  {
    BLI_assert(this->is_span());
    const CommonVArrayInfo info = this->get_impl()->common_info();
    return MutableSpan<T>(const_cast<T *>(static_cast<const T *>(info.data)), this->size());
  }
 
  void set(const int64_t index, T value)
  {
    BLI_assert(index >= 0);
    BLI_assert(index < this->size());
    this->get_impl()->set(index, std::move(value));
  }
 
  void set_all(Span<T> src)
  {
    BLI_assert(src.size() == this->size());
    this->get_impl()->set_all(src);
  }
 
  bool try_assign_GVMutableArray(GVMutableArray &varray) const
  {
    return this->get_impl()->try_assign_GVMutableArray(varray);
  }
 
 private:
  VMutableArrayImpl<T> *get_impl() const
  {
    /* This cast is valid by the invariant that a #VMutableArray->impl_ is always a
     * #VMutableArrayImpl. */
    return (VMutableArrayImpl<T> *)this->impl_;
  }
};
 
template<typename T> static constexpr bool is_VArray_v = false;
template<typename T> static constexpr bool is_VArray_v<VArray<T>> = true;
 
template<typename T> static constexpr bool is_VMutableArray_v = false;
template<typename T> static constexpr bool is_VMutableArray_v<VMutableArray<T>> = true;
 
template<typename T> class VArraySpan final : public Span<T> {
 private:
  VArray<T> varray_;
  Array<T> owned_data_;
 
 public:
  VArraySpan() = default;
 
  VArraySpan(const VArray<T> &varray) : VArraySpan(VArray<T>(varray)) {}
 
  VArraySpan(VArray<T> &&varray) : Span<T>(), varray_(std::move(varray))
  {
    if (!varray_) {
      return;
    }
    this->size_ = varray_.size();
    const CommonVArrayInfo info = varray_.common_info();
    if (info.type == CommonVArrayInfo::Type::Span) {
      this->data_ = static_cast<const T *>(info.data);
    }
    else {
      owned_data_.~Array();
      new (&owned_data_) Array<T>(varray_.size(), NoInitialization{});
      varray_.materialize_to_uninitialized(owned_data_);
      this->data_ = owned_data_.data();
    }
  }
 
  VArraySpan(VArraySpan &&other)
      : varray_(std::move(other.varray_)), owned_data_(std::move(other.owned_data_))
  {
    if (!varray_) {
      return;
    }
    this->size_ = varray_.size();
    const CommonVArrayInfo info = varray_.common_info();
    if (info.type == CommonVArrayInfo::Type::Span) {
      this->data_ = static_cast<const T *>(info.data);
    }
    else {
      this->data_ = owned_data_.data();
    }
    other.data_ = nullptr;
    other.size_ = 0;
  }
 
  VArraySpan &operator=(VArraySpan &&other)
  {
    if (this == &other) {
      return *this;
    }
    std::destroy_at(this);
    new (this) VArraySpan(std::move(other));
    return *this;
  }
};
 
namespace internal {
void print_mutable_varray_span_warning();
}
 
template<typename T> class MutableVArraySpan final : public MutableSpan<T> {
 private:
  VMutableArray<T> varray_;
  Array<T> owned_data_;
  bool save_has_been_called_ = false;
  bool show_not_saved_warning_ = true;
 
 public:
  MutableVArraySpan() = default;
 
  /* Create a span for any virtual array. This is cheap when the virtual array is a span itself. If
   * not, a new array has to be allocated as a wrapper for the underlying virtual array. */
  MutableVArraySpan(VMutableArray<T> varray, const bool copy_values_to_span = true)
      : MutableSpan<T>(), varray_(std::move(varray))
  {
    if (!varray_) {
      return;
    }
 
    this->size_ = varray_.size();
    const CommonVArrayInfo info = varray_.common_info();
    if (info.type == CommonVArrayInfo::Type::Span) {
      this->data_ = const_cast<T *>(static_cast<const T *>(info.data));
    }
    else {
      if (copy_values_to_span) {
        owned_data_.~Array();
        new (&owned_data_) Array<T>(varray_.size(), NoInitialization{});
        varray_.materialize_to_uninitialized(owned_data_);
      }
      else {
        owned_data_.reinitialize(varray_.size());
      }
      this->data_ = owned_data_.data();
    }
  }
 
  MutableVArraySpan(MutableVArraySpan &&other)
      : varray_(std::move(other.varray_)),
        owned_data_(std::move(other.owned_data_)),
        show_not_saved_warning_(other.show_not_saved_warning_)
  {
    if (!varray_) {
      return;
    }
 
    this->size_ = varray_.size();
    const CommonVArrayInfo info = varray_.common_info();
    if (info.type == CommonVArrayInfo::Type::Span) {
      this->data_ = static_cast<T *>(const_cast<void *>(info.data));
    }
    else {
      this->data_ = owned_data_.data();
    }
    other.data_ = nullptr;
    other.size_ = 0;
  }
 
  ~MutableVArraySpan()
  {
    if (varray_) {
      if (show_not_saved_warning_) {
        if (!save_has_been_called_) {
          internal::print_mutable_varray_span_warning();
        }
      }
    }
  }
 
  MutableVArraySpan &operator=(MutableVArraySpan &&other)
  {
    if (this == &other) {
      return *this;
    }
    std::destroy_at(this);
    new (this) MutableVArraySpan(std::move(other));
    return *this;
  }
 
  const VMutableArray<T> &varray() const
  {
    return varray_;
  }
 
  /* Write back all values from a temporary allocated array to the underlying virtual array. */
  void save()
  {
    save_has_been_called_ = true;
    if (this->data_ != owned_data_.data()) {
      return;
    }
    varray_.set_all(owned_data_);
  }
 
  void disable_not_applied_warning()
  {
    show_not_saved_warning_ = false;
  }
};
 
template<typename T> class SingleAsSpan {
 private:
  T value_;
  int64_t size_;
 
 public:
  SingleAsSpan(T value, int64_t size) : value_(std::move(value)), size_(size)
  {
    BLI_assert(size_ >= 0);
  }
 
  SingleAsSpan(const VArray<T> &varray) : SingleAsSpan(varray.get_internal_single(), varray.size())
  {
  }
 
  const T &operator[](const int64_t index) const
  {
    BLI_assert(index >= 0);
    BLI_assert(index < size_);
    UNUSED_VARS_NDEBUG(index);
    return value_;
  }
};
 
template<typename T> class VArrayRef {
 private:
  const VArray<T> &ref_;
 
 public:
  VArrayRef(const VArray<T> &ref) : ref_(ref) {}
 
  const T operator[](const int64_t index) const
  {
    return ref_[index];
  }
};
 
template<typename T, bool UseSingle, bool UseSpan> struct VArrayDevirtualizer {
  const VArray<T> &varray;
 
  template<typename Fn> bool devirtualize(const Fn &fn) const
  {
    const CommonVArrayInfo info = this->varray.common_info();
    const int64_t size = this->varray.size();
    if constexpr (UseSingle) {
      if (info.type == CommonVArrayInfo::Type::Single) {
        return fn(SingleAsSpan<T>(*static_cast<const T *>(info.data), size));
      }
    }
    if constexpr (UseSpan) {
      if (info.type == CommonVArrayInfo::Type::Span) {
        return fn(Span<T>(static_cast<const T *>(info.data), size));
      }
    }
    return false;
  }
};
 
template<typename T, typename Func>
inline void devirtualize_varray(const VArray<T> &varray, const Func &func, bool enable = true)
{
  if (enable) {
    if (call_with_devirtualized_parameters(
            std::make_tuple(VArrayDevirtualizer<T, true, true>{varray}), func))
    {
      return;
    }
  }
  func(VArrayRef<T>(varray));
}
 
template<typename T1, typename T2, typename Func>
inline void devirtualize_varray2(const VArray<T1> &varray1,
                                 const VArray<T2> &varray2,
                                 const Func &func,
                                 bool enable = true)
{
  if (enable) {
    if (call_with_devirtualized_parameters(
            std::make_tuple(VArrayDevirtualizer<T1, true, true>{varray1},
                            VArrayDevirtualizer<T2, true, true>{varray2}),
            func))
    {
      return;
    }
  }
  func(VArrayRef<T1>(varray1), VArrayRef<T2>(varray2));
}
 
}  // namespace blender