1 files changed, 67 insertions, 14 deletions

diff --git a/source/blender/blenlib/BLI_virtual_array.hh b/source/blender/blenlib/BLI_virtual_array.hh
index d0436bdc213..438fcc4b8f7 100644
--- a/source/blender/blenlib/BLI_virtual_array.hh
+++ b/source/blender/blenlib/BLI_virtual_array.hh
@@ -51,7 +51,10 @@ struct CommonVArrayInfo {
   /** True when the #data becomes a dangling pointer when the virtual array is destructed. */
   bool may_have_ownership = true;
 
-  /** Points either to nothing, a single value or array of values, depending on #type. */
+  /**
+   * Points either to nothing, a single value or array of values, depending on #type.
+   * If this is a span of a mutable virtual array, it is safe to cast away const.
+   */
   const void *data;
 
   CommonVArrayInfo() = default;
@@ -1117,16 +1120,19 @@ template<typename T> static constexpr bool is_VMutableArray_v<VMutableArray<T>>
  *    from faster access.
  *  - An API is called, that does not accept virtual arrays, but only spans.
  */
-template<typename T> class VArray_Span final : public Span<T> {
+template<typename T> class VArraySpan final : public Span<T> {
  private:
   VArray<T> varray_;
   Array<T> owned_data_;
 
  public:
-  VArray_Span() = default;
+  VArraySpan() = default;
 
-  VArray_Span(VArray<T> varray) : Span<T>(), varray_(std::move(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) {
@@ -1140,9 +1146,12 @@ template<typename T> class VArray_Span final : public Span<T> {
     }
   }
 
-  VArray_Span(VArray_Span &&other)
+  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) {
@@ -1155,25 +1164,25 @@ template<typename T> class VArray_Span final : public Span<T> {
     other.size_ = 0;
   }
 
-  VArray_Span &operator=(VArray_Span &&other)
+  VArraySpan &operator=(VArraySpan &&other)
   {
     if (this == &other) {
       return *this;
     }
     std::destroy_at(this);
-    new (this) VArray_Span(std::move(other));
+    new (this) VArraySpan(std::move(other));
     return *this;
   }
 };
 
 /**
- * Same as #VArray_Span, but for a mutable span.
+ * Same as #VArraySpan, but for a mutable span.
  * The important thing to note is that when changing this span, the results might not be
  * immediately reflected in the underlying virtual array (only when the virtual array is a span
  * internally). The #save method can be used to write all changes to the underlying virtual array,
  * if necessary.
  */
-template<typename T> class VMutableArray_Span final : public MutableSpan<T> {
+template<typename T> class MutableVArraySpan final : public MutableSpan<T> {
  private:
   VMutableArray<T> varray_;
   Array<T> owned_data_;
@@ -1181,11 +1190,17 @@ template<typename T> class VMutableArray_Span final : public MutableSpan<T> {
   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. */
-  VMutableArray_Span(VMutableArray<T> varray, const bool copy_values_to_span = true)
+  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) {
@@ -1204,15 +1219,53 @@ template<typename T> class VMutableArray_Span final : public MutableSpan<T> {
     }
   }
 
-  ~VMutableArray_Span()
+  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 (show_not_saved_warning_) {
-      if (!save_has_been_called_) {
-        std::cout << "Warning: Call `save()` to make sure that changes persist in all cases.\n";
+    if (varray_) {
+      if (show_not_saved_warning_) {
+        if (!save_has_been_called_) {
+          std::cout << "Warning: Call `save()` to make sure that changes persist in all cases.\n";
+        }
       }
     }
   }
 
+  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()
   {