BLI: support value initialization in CPPType

Value initialization differs from default-construction in that it
also zero-initializes trivial types.

source/blender/blenlib/BLI_cpp_type.hh

@@ -110,6 +110,9 @@ class CPPType : NonCopyable, NonMovable {
   void (*default_construct_)(void *ptr) = nullptr;
   void (*default_construct_indices_)(void *ptr, IndexMask mask) = nullptr;
 
+  void (*value_initialize_)(void *ptr) = nullptr;
+  void (*value_initialize_indices_)(void *ptr, IndexMask mask) = nullptr;
+
   void (*destruct_)(void *ptr) = nullptr;
   void (*destruct_indices_)(void *ptr, IndexMask mask) = nullptr;
 
@@ -325,6 +328,31 @@ class CPPType : NonCopyable, NonMovable {
     default_construct_indices_(ptr, mask);
   }
 
+  /**
+   * Same as #default_construct, but does zero initialization for trivial types.
+   *
+   * C++ equivalent:
+   *   new (ptr) T();
+   */
+  void value_initialize(void *ptr) const
+  {
+    BLI_assert(this->pointer_can_point_to_instance(ptr));
+
+    value_initialize_(ptr);
+  }
+
+  void value_initialize_n(void *ptr, int64_t n) const
+  {
+    this->value_initialize_indices(ptr, IndexMask(n));
+  }
+
+  void value_initialize_indices(void *ptr, IndexMask mask) const
+  {
+    BLI_assert(mask.size() == 0 || this->pointer_can_point_to_instance(ptr));
+
+    value_initialize_indices_(ptr, mask);
+  }
+
   /**
    * Call the destructor on the given instance of this type. The pointer must not be nullptr.
    *

source/blender/blenlib/BLI_cpp_type_make.hh

@@ -20,6 +20,16 @@ template<typename T> void default_construct_indices_cb(void *ptr, IndexMask mask
   mask.foreach_index([&](int64_t i) { new (static_cast<T *>(ptr) + i) T; });
 }
 
+template<typename T> void value_initialize_cb(void *ptr)
+{
+  new (ptr) T();
+}
+
+template<typename T> void value_initialize_indices_cb(void *ptr, IndexMask mask)
+{
+  mask.foreach_index([&](int64_t i) { new (static_cast<T *>(ptr) + i) T(); });
+}
+
 template<typename T> void destruct_cb(void *ptr)
 {
   (static_cast<T *>(ptr))->~T();
@@ -186,6 +196,8 @@ CPPType::CPPType(CPPTypeParam<T, Flags> /* unused */, StringRef debug_name)
   if constexpr (std::is_default_constructible_v<T>) {
     default_construct_ = default_construct_cb<T>;
     default_construct_indices_ = default_construct_indices_cb<T>;
+    value_initialize_ = value_initialize_cb<T>;
+    value_initialize_indices_ = value_initialize_indices_cb<T>;
     static T default_value;
     default_value_ = (void *)&default_value;
   }

source/blender/blenlib/tests/BLI_cpp_type_test.cc

@@ -118,6 +118,40 @@ TEST(cpp_type, DefaultConstruction)
   EXPECT_EQ(buffer[8], 0);
 }
 
+TEST(cpp_type, DefaultConstructTrivial)
+{
+  int value = 5;
+  CPPType::get<int>().default_construct(&value);
+  EXPECT_EQ(value, 5);
+}
+
+TEST(cpp_type, ValueInitialize)
+{
+  int buffer[10] = {0};
+  CPPType_TestType.value_initialize((void *)buffer);
+  EXPECT_EQ(buffer[0], default_constructed_value);
+  EXPECT_EQ(buffer[1], 0);
+  CPPType_TestType.value_initialize_n((void *)buffer, 3);
+  EXPECT_EQ(buffer[0], default_constructed_value);
+  EXPECT_EQ(buffer[1], default_constructed_value);
+  EXPECT_EQ(buffer[2], default_constructed_value);
+  EXPECT_EQ(buffer[3], 0);
+  CPPType_TestType.value_initialize_indices((void *)buffer, {2, 5, 7});
+  EXPECT_EQ(buffer[2], default_constructed_value);
+  EXPECT_EQ(buffer[4], 0);
+  EXPECT_EQ(buffer[5], default_constructed_value);
+  EXPECT_EQ(buffer[6], 0);
+  EXPECT_EQ(buffer[7], default_constructed_value);
+  EXPECT_EQ(buffer[8], 0);
+}
+
+TEST(cpp_type, ValueInitializeTrivial)
+{
+  int value = 5;
+  CPPType::get<int>().value_initialize(&value);
+  EXPECT_EQ(value, 0);
+}
+
 TEST(cpp_type, Destruct)
 {
   int buffer[10] = {0};