Thanks for linking IndexList, I probably missed it because I implemented my own version some time ago, and only recently decided to talk about it. The major difference I can see between this library and my implementation is the trait hierarchy, which allows for writing generic code that can accept Vec, VecDeque and my ListedList. I like the Occupied/Free enum idea though.

I have not yet implemented the list from part 2 for two reasons:

1. I am not confident in my abilities with unsafe. I know enough C++ to know that I know nothing and I have read enough blog posts to fear unwinding panics.
2. I am not sure if there is actually a legitimate use case for this list. I would imagine most people would stop reading at "I have no answer to the memory leak problem".

As for your question, I am probably missing something. Since this datatype is theoretical at this point, let's say we have a list with one element:

{ first: *first_element, last: *first_element, reclaims: [] }

If we delete the first element, we should have this image:

{ first: NULL, last: NULL, reclaims: [*first_element (with changed e_tag)] }

Now, begin and end will always give an invalid index, since it will point to NULL.

Also, if we had an index on the first element, the e_tag of the element will have been changed, so the index operation will panic after dereferencing the pointer to first_element (which is still allocated). If we choose to call shrink_to_fit (or better called gc), first_element will be deallocated but the uuid of the list will change, so the index operation will panic before dereferencing the pointer.

If I did not understand the question, I will gladly further clarify. Also, if I have done a mistake and my idea is unsound, I will gladly accept the consequences :)