Re: some trivial questions?

[Blady <p.p11@orange.fr>]

Le mercredi 22 novembre 2017 01:56:29 UTC+1, Randy Brukardt a écrit :
<...>
> Similar issues have occurred for every version of Ada since. (Attempts to 
> fix the problem of tagged derived types in generic units among others have 
> died because of compatibility concerns. Similarly, my attempt to allow 
> untagged type declarations in the private part of protected types seems to 
> have died for that reason, even though it's not possible for there to be an 
> incompatibility [I think]. I think there is a currently open AI that 
> probably will be eventually dropped because of compatibility concerns, 
> rather than making it into Ada 2020. And so it goes...)
<...>
>                                    Randy.

Hello,
Avoiding compatibility issues is mostly a concern for customers of existing commercial Ada compilers.

Here is the Ada standard implementation of some commercial Ada compilers:
AdaCore: Ada 2012
PTC ObjectAda (Atego): Ada 2005
PTC ApexAda (Rational): Ada 2005
DDC International: Ada 95
Green Hills Software: Ada 95
Irvine Compiler Corporation: Ada 95 (Ada 2005 is in limited beta testing)
OC-Systems: Ada 95
RR Software: Ada 95 (selected Ada 2007 features)
XGC: Ada 95
SCORE Ada DDC-I: Ada 95
XD Ada DXC Technology: Ada 95
(Please correct if I'm wrong)
(see full list with WEB link on http://www.adalog.fr/fr/outils_payants.html)
I'm quite surprise not to find some still with Ada 83, maybe old DEC or IBM ones.

In 2017, why aren't they all at Ada 2012 standard?
One clue may be that customers which are mainly conservative (Spatial, Aeronautics, Defense... domains) are not so demanding. Remember "The demand makes the offer".
Then the evolution process is made of small compatible changes to be attractive to customers and then compiler providers.
But in majority they don't upgrade!
Thus who cares about being compatible for new standard?
So go on attractive changes, more fashionable some people says disruptive changes, with possibly compatibility issues that may fixed after.
The point is that some duration is mandatory to analyse true effects of compatibility issues and after make them residuals.
Thus when commercial compiler providers and their customers are well aware of residuals issues they can decide to upgrade (or not) for stable attractive features.
Surely idealistic point of view ;-)
Actually, it is a question of trade off, maybe the present cursor position is too conservative.
Regards Pascal.