Re: += in ada

["Alexandre E. Kopilovitch" <aek@vib.usr.pu.ru>]

Robert I. Eachus wrote:

> > So, Robert and/or "Bob", would it be acceptable to the Guardians Of Ada's
> > Purity if the semantics of a new "idem" feature were to specify that:
> >    x := f(idem);
> > could leave an arbitrary value in x in the event of a Constraint_Error being
> > raised; thus always permitting an update-in-place implementation?
>
> Robert would say no, Bob would say yes.  The ARG would spend a couple of 
> hours discussing it and not change the current situation. ;-)  In other 
> words, right now IF you need to you can write things so that x won't get 
> corrupted.  Also you will normally get the fastest possible code 
> generated.  It is only when those two principles collide that there is 
> an issue.  Robert was happier with the Ada 83 rules.  Bob prefers the 
> Ada 95 rules.  But in 90+ percent of the cases where Constraint_Error 
> can occur, there are no practical differences between the rules.

Isn't it exactly one of the situations for which pragmas exist? Both sides
have their good arguments (which are adequate for different circumstances),
battlefield is isolated, and collisions are relatively rare. Why not (as all
these conditions are established) introduce a pragma and thus close the issue?



Alexander Kopilovitch                      aek@vib.usr.pu.ru
Saint-Petersburg
Russia