Survey : use of limited private types

Survey : use of limited private types

[Stef Van Vlierberghe]

A few weeks ago on the ISO-WG9 meeting on the Ada9X project,
I tried  to  reraise  the  issue  of  type  abstraction  and
user-defined  assignment.  The  "answer"  seemed  to be "use
limited  types, export  procedure  ASSIGN, and live with all
the  known   limitations   of  limited   types",  since  for
non-published    reasons   "user-defined    assignment   was
considered  too  complex an issue".  A reference  to the C++
support for the paradigm invoked only adverse response.

Therefore a little  survey.  Everyone  that replies by email
will receive a report that  summarizes  all  replies, so you
can directly  reply to  stef@cfmu.eurocontrol.be  or post of
follow-up article.

I have major  difficulty  selling the answer quoted above in
our  environment.  Most programmers had a little  experience
with limited  types,  enough to scare them off, and are very
reluctant  to try once  more.  Has  anyone  experience  with
abstract  data types  that need  control  over  equality  or
assignment?  Were  limited  types  used in this case (as the
"answer"  above  suggests)?  Or did you  simply  rely or the
predefined assignment not being used?

Do you use  components  that do not support  generic  formal
limited types (such as most Booch components), or do you use
components   that  do  ?  Were  these  acquired   externally
(reference  if possible) or  developed  in-house  (sample or
spec if possible) ?

Do  you  know  of  any  published   information   about  the
INFEASIBILITY of user-defined assignment?

-- 
Stef VAN VLIERBERGHE            Eurocontrol - Central Flow Management Unit
stef@cfmu.eurocontrol.be        Avenue des Arts 19H
Tel: +32 2 729 33 42            B-1040 BRUSSELS
Fax: +32 2 729 32 16            Belgium