RE: List container: Insert and Delete

["Steven Deller" <deller@smsail.com>]

> -----Original Message-----
> From: comp.lang.ada-admin@ada.eu.org 
> > However, I'm pretty sure that trying to do insertions and deletions 
> > while iterating through a list fails both (a) and (b) miserably. 
> > That's what I was trying to get across.
> 
> I agree that one should not be doing insertions and deletions 
> while iterating over a list. Iterators should not allow this, 
> and positions should generally not be used for iteration.
> 
> -- 
> Jeff Carter

I don't understand this comment.  It seems to me that iteration to find
some value and then insertion at that point is a normal list operation.

I see no difficulty with iteration doing inserts and deletes, even with
other simultaneous iterators.  It is a simple matter to define the
semantics to be unambiguous, particularly if you use positions that are
"in between" elements and semantics like:
   delete following item
   delete preceding item
   get value of following item
   get value of preceding item
   move to next position (skip over an element)
   move to previous position (skip backwards over an element)
   goto head of list (position before first item)
   goto tail of list (position after last item)
   is at end of list (boolean)
   is at beginning of list (boolean)

These are all well defined, even for empty lists.

Regards,
Steve Deller