Function: add method to create shallow copy of virtual array

Creating a shallow copy is sometimes useful to get a unique ptr
for a virtual array when one only has a reference. It shouldn't
be used usually, but sometimes its the fastest way to do correct
ownership handling.

source/blender/functions/FN_generic_virtual_array.hh

@@ -34,6 +34,12 @@ namespace blender::fn {
 template<typename T> class GVArray_Typed;
 template<typename T> class GVMutableArray_Typed;
 
+class GVArray;
+class GVMutableArray;
+
+using GVArrayPtr = std::unique_ptr<GVArray>;
+using GVMutableArrayPtr = std::unique_ptr<GVMutableArray>;
+
 /* A generically typed version of `VArray<T>`. */
 class GVArray {
  protected:
@@ -143,6 +149,8 @@ class GVArray {
     return GVArray_Typed<T>(*this);
   }
 
+  GVArrayPtr shallow_copy() const;
+
  protected:
   virtual void get_impl(const int64_t index, void *r_value) const;
   virtual void get_to_uninitialized_impl(const int64_t index, void *r_value) const = 0;
@@ -215,9 +223,6 @@ class GVMutableArray : public GVArray {
   virtual void *try_get_internal_mutable_varray_impl();
 };
 
-using GVArrayPtr = std::unique_ptr<GVArray>;
-using GVMutableArrayPtr = std::unique_ptr<GVMutableArray>;
-
 class GVArray_For_GSpan : public GVArray {
  protected:
   const void *data_ = nullptr;

source/blender/functions/intern/generic_virtual_array.cc

@@ -18,6 +18,37 @@
 
 namespace blender::fn {
 
+/* --------------------------------------------------------------------
+ * GVArray_For_ShallowCopy.
+ */
+
+class GVArray_For_ShallowCopy : public GVArray {
+ private:
+  const GVArray &varray_;
+
+ public:
+  GVArray_For_ShallowCopy(const GVArray &varray)
+      : GVArray(varray.type(), varray.size()), varray_(varray)
+  {
+  }
+
+ private:
+  void get_impl(const int64_t index, void *r_value) const override
+  {
+    varray_.get(index, r_value);
+  }
+
+  void get_to_uninitialized_impl(const int64_t index, void *r_value) const override
+  {
+    varray_.get_to_uninitialized(index, r_value);
+  }
+
+  void materialize_to_uninitialized_impl(const IndexMask mask, void *dst) const override
+  {
+    varray_.materialize_to_uninitialized(mask, dst);
+  }
+};
+
 /* --------------------------------------------------------------------
  * GVArray.
  */
@@ -73,6 +104,26 @@ const void *GVArray::try_get_internal_varray_impl() const
   return nullptr;
 }
 
+/**
+ * Creates a new `std::unique_ptr<GVArray>` based on this `GVArray`.
+ * The lifetime of the returned virtual array must not be longer than the lifetime of this virtual
+ * array.
+ */
+GVArrayPtr GVArray::shallow_copy() const
+{
+  if (this->is_span()) {
+    return std::make_unique<GVArray_For_GSpan>(this->get_internal_span());
+  }
+  if (this->is_single()) {
+    BUFFER_FOR_CPP_TYPE_VALUE(*type_, buffer);
+    this->get_internal_single(buffer);
+    std::unique_ptr new_varray = std::make_unique<GVArray_For_SingleValue>(*type_, size_, buffer);
+    type_->destruct(buffer);
+    return new_varray;
+  }
+  return std::make_unique<GVArray_For_ShallowCopy>(*this);
+}
+
 /* --------------------------------------------------------------------
  * GVMutableArray.
  */