From c772461741462a8c0b83309676a49e41eb0e81cc Mon Sep 17 00:00:00 2001
From: Sergey Sharybin <sergey@blender.org>
Date: Tue, 29 Mar 2022 10:53:25 +0200
Subject: Cleanup: Use higher level semantic for zeroing DNA objects in C++

Replaces old-style memzero-style of call with zero-initializer.
Allows to shorten typical initialization code to a single line:

  Object foo = blender::dna::shallow_zero_initialize<Object>()

This will allow to more easily convert designated initializer
which is often used to fill object with zeroes to the explicit
function calls:

  MyDNAStruct foo = {};

will be translated to

  MyDNAStruct foo = blender::dna::shallow_zero_initialize<MyDNAStruct>();

Differential Revision: https://developer.blender.org/D14486
---
 source/blender/makesdna/DNA_defs.h | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

(limited to 'source/blender/makesdna/DNA_defs.h')

diff --git a/source/blender/makesdna/DNA_defs.h b/source/blender/makesdna/DNA_defs.h
index 79477a56695..bbce4839506 100644
--- a/source/blender/makesdna/DNA_defs.h
+++ b/source/blender/makesdna/DNA_defs.h
@@ -86,6 +86,9 @@ template<class T> class ShallowDataConstRef {
   const T &ref_;
 };
 
+template<class T> class ShallowZeroInitializeTag {
+};
+
 }  // namespace blender::dna::internal
 
 #  define DNA_DEFINE_CXX_METHODS(class_name) \
@@ -108,6 +111,18 @@ template<class T> class ShallowDataConstRef {
         _DNA_internal_memcpy(this, ref.get_pointer(), sizeof(class_name)); \
       } \
       return *this; \
+    } \
+    /* Create object which memory is filled with zeros. */ \
+    class_name(const blender::dna::internal::ShallowZeroInitializeTag<class_name> /*tag*/) \
+        : class_name() \
+    { \
+      _DNA_internal_memzero(this, sizeof(class_name)); \
+    } \
+    class_name &operator=( \
+        const blender::dna::internal::ShallowZeroInitializeTag<class_name> /*tag*/) \
+    { \
+      _DNA_internal_memzero(this, sizeof(class_name)); \
+      return *this; \
     }
 
 namespace blender::dna {
@@ -126,11 +141,12 @@ template<class T>
   return internal::ShallowDataConstRef(other);
 }
 
-/* Fill underlying memory used by DNA object with zeroes. */
-template<class T> inline void zero_memory(T &object)
+/* DNA object initializer which leads to an object which underlying memory is filled with zeroes.
+ */
+template<class T>
+[[nodiscard]] inline internal::ShallowZeroInitializeTag<T> shallow_zero_initialize()
 {
-  /* TODO(sergey): Consider adding static assert for T being a trivial type. */
-  _DNA_internal_memzero(&object, sizeof(T));
+  return internal::ShallowZeroInitializeTag<T>();
 }
 
 }  // namespace blender::dna
-- 
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