Just like doubly linked list(e.g. std::LinkedList), but supports that returning a index of the vec when push. And you can remove an element by a valid index. Enhanced Edition of slab crate.

• push_back()/push_front()
• get()/get_mut()/[]/[mut]
• front()/front_mut()/back()/back_mut()
• pop_front()/pop_back()

All operations above are O(1) worst time complexity, except pushs are average O(1).

You can also use some like as a Map which the key is always usize.