[Question] Why Cleanup Functions in Iterator are registered in a wired way ?

[TDAkory]

I've read some source code of Iterator and having this confusion about Iterator::RegisterCleanup

void Iterator::RegisterCleanup(CleanupFunction func, void* arg1, void* arg2) {
  assert(func != nullptr);
  CleanupNode* node;
  if (cleanup_head_.IsEmpty()) {
    node = &cleanup_head_;
  } else {
    node = new CleanupNode();
    node->next = cleanup_head_.next;
    cleanup_head_.next = node;
  }
  node->function = func;
  node->arg1 = arg1;
  node->arg2 = arg2;
}

Let's say I want to register multiple cleanup functions in an Iterator.

• The first function will be in cleanuphead, the first place of linked list
• The second function will be in cleanuphead.next, the second place of linked list, which is fine by now
• But the third function will be in cleanuphead.next, the second place of linked list, so far and so forth, why do insertion always happens in the second place of linked list?

If I'm understanding it right: If we registered 4 cleanup functions like [A,B,C,D] , it will called in a sequence like [A, D, C, B] I demonstrated it here :https://godbolt.org/z/Kf6YYfnKn

what's the design thoughts here?