Re: Is 'out' different from 'in out' (Was: Uninitialized "out" parameters)

[gauthier@unilim.fr (Michel Gauthier)]

Thanks to dewar@cs.nyu.edu (Robert Dewar),
      stt@henning.camb.inmet.com (Tucker Taft) and
      bobduff@world.std.com (Robert A Duff) 
          for their answers to my initial posting :  

>>  [...]  
>>  So, I repost the question in another form :
>>  ___is there a difference between 'out' and 'in out' parameters ?___
>>  [...]

They all confirm what I was not entirely sure to understand correctly.
There is no essential difference between 'out' and 'in out' parameters,
and it is probably worth considering them to be the same thing.

IMHO, it was a mistake of the 9X design. It's too late to repair.

Possible useful style rule : avoid 'out' parameters, since they
are error-prone, and prefer 'in out'.

-----

In article <Duy5JB.3o@world.std.com>, Bob Duff wrote:

>> [...]
>>  
>>  Well, it's not a *compiler* issue -- the RM says it.

Agreed with, but I guess nobody assumes that "LRM says"
always implies "all validated compilers do".
By all the ancient Greeks' gods, it would be great if it were true !
Apologies if no explicit compiler names are given here.
  
>>  [...]
>>
>>  Note that in Ada 83, your intuitive view was not true.  One such case is
>>  when the formal is an unconstrained array.  In that case, the bounds of
>>  the array are passed IN, even if the mode is OUT.  For your intuitive
>>  view to work, Ada would have to have truly dynamic arrays (that is,
>>  arrays that can change size on assignment).  Discriminants are similar
>>  to array bounds.

Another view is that bounds and discriminants are properties of the
_variable_ itself, always of mode 'in', and that the mode is a
property of the contents. Possibly formally dubious, but didactically
useful.

-----

In article <DuyC0H.6Fr.0.-s@inmet.camb.inmet.com>,
stt@henning.camb.inmet.com (Tucker Taft) wrote:

>>  Michel Gauthier (gauthier@unilim.fr) wrote:
>>  [...]  
>>  : ___is an 'out' controlled object finalised and reinitialised when entering
>>  : the subprogram ?___
>>  
>>  No; controlled types are always passed by reference.

Parameter passing has _nothing_ to deal with where the
finalisation takes place, either as a preliminary phase of
calling (strict 'out' behaviour) or as part of the first
later assignment (LRM 'in out'-like behaviour).

Possible interpretation of the debate : my view is at a higher level
(in the programming sense) than Bob's and Tuck's, which yields a
false appearence of disagreeing.

>>  [...]   
>>  : Finally, ___an AI discussion might be envisaged___. Don't you think so ?
>>  
>>  AI meaning "artificial intelligence"? ;-)  Or AI meaning Ada Interpretation?

" Ada Interpretation", of course. But all answers converge to 
no doubt in interpretation. So, I remove the suggestion.

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