BLI: improve constructors and conversions to span

This allows us to avoid many calls to `as_span()` methods. I will
remove those in the next commit. Furthermore, constructors
of Vector and Array can convert from one type to another now.

I tested these changes on Linux with gcc and on Windows.

1 files changed, 36 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_memory_utils.hh b/source/blender/blenlib/BLI_memory_utils.hh
index 16d6227a551..133615f0f31 100644
--- a/source/blender/blenlib/BLI_memory_utils.hh
+++ b/source/blender/blenlib/BLI_memory_utils.hh
@@ -26,6 +26,7 @@
 
 #include <memory>
 #include <new>
+#include <type_traits>
 
 #include "BLI_utildefines.h"
 
@@ -135,6 +136,32 @@ template<typename T> void uninitialized_copy_n(const T *src, uint n, T *dst)
 }
 
 /**
+ * Convert n values from type `From` to type `To`.
+ *
+ * Exception Safety: Strong.
+ *
+ * Before:
+ *  src: initialized
+ *  dst: uninitialized
+ * After:
+ *  src: initialized
+ *  dst: initialized
+ */
+template<typename From, typename To> void uninitialized_convert_n(const From *src, uint n, To *dst)
+{
+  uint current = 0;
+  try {
+    for (; current < n; current++) {
+      new ((void *)(dst + current)) To((To)src[current]);
+    }
+  }
+  catch (...) {
+    destruct_n(dst, current);
+    throw;
+  }
+}
+
+/**
  * Move n values from src to dst.
  *
  * Exception Safety: Basic.
@@ -364,6 +391,15 @@ template<typename T, size_t Size = 1> class TypedBuffer {
 class NoInitialization {
 };
 
+/**
+ * Helper variable that checks if a pointer type can be converted into another pointer type without
+ * issues. Possible issues are casting away const and casting a pointer to a child class.
+ * Adding const or casting to a parent class is fine.
+ */
+template<typename From, typename To>
+inline constexpr bool is_convertible_pointer_v =
+    std::is_convertible_v<From, To> &&std::is_pointer_v<From> &&std::is_pointer_v<To>;
+
 }  // namespace blender
 
 #endif /* __BLI_MEMORY_UTILS_HH__ */