Implement C++ methods for DNA structures

This change makes it possible to add implementation of common
C++ methods for DNA structures which helps ensuring unsafe
operations like shallow copy are done explicitly.

For example, creating a shallow copy used to be:

  Object temp_object = *input_object;

In the C++ context it was seen like the temp_object is
properly decoupled from the input object, while in the
reality is it not. Now this code becomes:

  Object temp_object = blender::dna::shallow_copy(*input_object);

The copy and move constructor and assignment operators are
now explicitly disabled.

Other than a more explicit resource management this change
also solves a lot of warnings generated by the implicitly
defined copy constructors w.r.t dealing with deprecated fields.
These warnings were generated by Apple Clang when a shallow
object copy was created via implicitly defined copy constructor.

In order to enable C++ methods for DNA structures a newly added
macro `DNA_DEFINE_CXX_METHODS()` is to be used:

  tpyedef struct Object {
    DNA_DEFINE_CXX_METHODS(Object)
    ...
  } Object;

For the shallow copy use `blender::dna::shallow_copy()`.

The implementation of the memcpy is hidden via an internal DNA
function to avoid pulling `string.h` into every DNA header.
This means that the solution does not affect on the headers
dependencies.

---

Ideally `DNA_shallow_copy` would be defined in a more explicit
header, but don;t think we have a suitable one already. Maybe
we can introduce `DNA_access.h` ?

Differential Revision: https://developer.blender.org/D14427

1 files changed, 12 insertions, 0 deletions

diff --git a/source/blender/makesdna/intern/dna_utils.c b/source/blender/makesdna/intern/dna_utils.c
index 8c86ef69ebd..560b91b925e 100644
--- a/source/blender/makesdna/intern/dna_utils.c
+++ b/source/blender/makesdna/intern/dna_utils.c
@@ -308,3 +308,15 @@ const char *DNA_struct_rename_legacy_hack_alias_from_static(const char *name)
 }
 
 /** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Internal helpers for C++
+ * \{ */
+
+void _DNA_internal_memcpy(void *dst, const void *src, size_t size);
+void _DNA_internal_memcpy(void *dst, const void *src, const size_t size)
+{
+  memcpy(dst, src, size);
+}
+
+/** \} */