Log for the design of a statically safe list<J*>

23.05

Yesterday, I thought that the current_ member of JList::iterator poses me a problem, which I cannot quite find again today:

• I have to compare it when comparing iterators (two iterators could differ only by their current_ member)
• To detect that a list is empty, one can only compare the begin() and end() iterators for equality.
• Thus, iterators pointing at the beginning or the end of an empty list must be identical.
• I am allowed to invalidate iterators pointing to the element I am erasing. If I erase the last element (the list becomes empty), I don't care for iterators pointing at it.
• True, but I do care for an iterator that would be pointing past it, i.e. at the end of the list. And I am not allowed to modify it. I.e. its current_ must not change because the list becomes empty.
• Therefore, there cannot be a special empty_ state in the Current enum (the solution followed yesterday in the /main branch).
• Furthermore, the iterator returned by end() must have a fixed current_ value (conventionally, string_).
• Therefore, the iterator returned by begin() from an empty list must have the same current_ value (string_).

I initiated yesterday 2 alternative modification strategies:

• the one based on an empty_ state (in the /main branch) is clearly wrong;
• the other (in a no_current branch) is not definitely to be abandoned, but is only an option. I leave it for now (both incompleted and in error!)

I continue thus for now on the /main branch, but undo the empty_ changes.

Completed, built: it works.
Labelled MARC-JLIST-002.