@@ -118,3 +115,1 @@
-                 '.',
-                 offsetof(BoneCollection, name),
-                 sizeof(bcoll->name));
+  struct DupNameCheckData {

@@ -121,0 +143,4 @@
+ * This means, for example, that for a collection array of length N, you can
+ * pass N as the index to append to the end.
+ */
+static void bonecoll_insert_at_index(bArmature *armature, BoneCollection *bcoll, int index)

@@ -121,0 +185,4 @@
+ */
+static BoneCollection *bonecoll_remove(bArmature *armature, int index)
+{
+  BLI_assert(index < armature->collection_array_num);

@@ -121,0 +202,4 @@
+  armature->collection_array[armature->collection_array_num] = nullptr;
+
+  /* Update the active BoneCollection. */
+  int new_active_index = armature->runtime.active_collection_index;

@@ -121,0 +219,4 @@
+static int bonecoll_find_index(const bArmature *armature, const BoneCollection *bcoll)
+{
+  int index = 0;
+  while (index < armature->collection_array_num && armature->collection_array[index] != bcoll) {

@@ -155,2 +266,3 @@
 
-  BLI_insertlinkafter(&armature->collections, anchor, bcoll);
+  const int anchor_index = bonecoll_find_index(armature, anchor);
+  BLI_assert(anchor_index >= 0);

@@ -224,19 +332,63 @@ bool ANIM_armature_bonecoll_is_editable(const bArmature *armature, const BoneCol
   return true;
 }
 
+bool ANIM_armature_bonecoll_move_to_index(bArmature *armature, int from_index, int to_index)

@@ -227,0 +345,4 @@
+  /* Shift collections over to fill the gap at from_index and make room at to_index. */
+  {
+    BoneCollection **start = armature->collection_array + std::min(from_index, to_index);
+    const size_t count = std::max(from_index, to_index) - std::min(from_index, to_index);

@@ -272,3 +424,3 @@
   }
 
-  BLI_remlink_safe(&armature->collections, bcoll);
+  bonecoll_remove(armature, bonecoll_find_index(armature, bcoll));

@@ -535,2 +682,2 @@
-blender::Map<BoneCollection *, BoneCollection *> ANIM_bonecoll_listbase_copy_no_membership(
-    ListBase *bone_colls_dst, ListBase *bone_colls_src, const bool do_id_user)
+blender::Map<BoneCollection *, BoneCollection *> ANIM_bonecoll_array_copy_no_membership(
+    BoneCollection ***bcoll_array_dst,

@@ -537,0 +683,4 @@
+    BoneCollection ***bcoll_array_dst,
+    int *bcoll_array_dst_num,
+    BoneCollection **bcoll_array_src,
+    int bcoll_array_src_num,

@@ -539,3 +695,3 @@
 
   blender::Map<BoneCollection *, BoneCollection *> bcoll_map{};
-  LISTBASE_FOREACH (BoneCollection *, bcoll_src, bone_colls_src) {
+  for (int i = 0; i < *bcoll_array_dst_num; i++) {

@@ -63,2 +65,2 @@
-    LISTBASE_FOREACH_BACKWARD_MUTABLE (BoneCollection *, bcoll, &arm.collections) {
-      ANIM_armature_bonecoll_remove(&arm, bcoll);
+    while (arm.collection_array_num > 0) {
+      ANIM_armature_bonecoll_remove(&arm, arm.collection_array[arm.collection_array_num - 1]);

@@ -146,0 +142,4 @@
+    armature_dst->collection_array = static_cast<BoneCollection **>(
+        MEM_dupallocN(armature_src->collection_array));
+    armature_dst->collection_array_num = armature_src->collection_array_num;
+    for (int i = 0; i < armature_dst->collection_array_num; i++) {

@@ -146,0 +143,4 @@
+        MEM_dupallocN(armature_src->collection_array));
+    armature_dst->collection_array_num = armature_src->collection_array_num;
+    for (int i = 0; i < armature_dst->collection_array_num; i++) {
+      armature_dst->collection_array[i] = static_cast<BoneCollection *>(

@@ -171,1 +179,3 @@
-    }
+  if (armature->collection_array) {
+    for (BoneCollection *bcoll : armature->collections_span()) {
+      /* ID properties. */

@@ -303,0 +333,4 @@
+
+  /* Restore the BoneCollection array and clear the listbase. */
+  arm->collection_array = collection_array_backup;
+  if (arm->collection_array_num > 0) {

@@ -336,0 +384,4 @@
+      arm->collection_array_num, sizeof(BoneCollection *), __func__);
+  {
+    int i = 0;
+    LISTBASE_FOREACH (BoneCollection *, bcoll, &arm->collections) {

@@ -3043,0 +3111,4 @@
+
+blender::Span<const BoneCollection *> bArmature::collections_span() const
+{
+  if (collection_array == nullptr || collection_array_num <= 0) {

@@ -74,3 +74,3 @@
   char active_collection_name[MAX_NAME];
   ListBase /* EditBone */ ebones;
-  ListBase /* BoneCollection */ bone_collections;
+  BoneCollection **collection_array;

@@ -143,3 +150,3 @@
                        BLI_listbase_count(&ebone->bone_collections);
   }
-  uarm->undo_size += sizeof(BoneCollection) * BLI_listbase_count(&uarm->bone_collections);
+  uarm->undo_size += (sizeof(BoneCollection) + sizeof(BoneCollection *)) *

@@ -344,3 +341,1 @@
-
-          bone_collection_by_name.add(bcoll->name, bcoll);
-          mapped = bcoll;
+          BoneCollection *new_bcoll = ANIM_armature_bonecoll_new(arm, bcoll->name);