Re: Bug or feature?

[Adam Beneschan <adambeneschan@gmail.com>]

On Wednesday, May 14, 2014 2:24:57 PM UTC-7, Laurent wrote:

> Modified my little test with Result:= 2_000_000_000 + 2_000_000_000;
> Doesn't compile:
> 
> /Volumes/Kingston/GPS/Chapter 14/buffer_overflow.adb
>         11:27 static expression fails Constraint_Check
>         11:27 value not in range of type "Standard.Integer"

Yes, you have to use variables.  2_000_000_000 + 2_000_000_000 is a static expression that can be computed at compile-time, and some of the checks that would normally cause exceptions at run-time will cause errors at compile-time, due to special rules in the language about static expressions.

                            
> So it is a bug?  Or just a matter of putting an additional flag?

The requirement to add -gnato to get full checking has been discussed quite a bit on this newsgroup and elsewhere.  Basically, overflow checking adds a lot of code on most processors, and I think the decision was made early on to disable it by default.  Not everyone likes this.  It looks like there's a bug in how range checking is handled if -gnato isn't used, over and above the lack of overflow checking.  But it appears to be a bug that cannot come up if -gnato is used.

                            -- Adam