Re: Ada safety road Was: Which is right ...

[Tucker Taft <stt@averstar.com>]

Robert Dewar wrote:
> 
> In article <yeclndu44z8.fsf@king.cts.com>,
>   Keith Thompson <kst@cts.com> wrote:
> > This is why the authors of Ada (both 83 and 95) made such an
> > effort to minimize the number of cases where this can happen,
> > and to clearly document the cases that couldn't reasonably be
> > avoided.
> 
> I think more could have been done, particularly in the area
> of uninitialized variables. 

Using an uninitialized variable is *not* erroneous in Ada 95.

> ... For simple variables, I like the
> CDL approach which says that there must not exist any static
> paths through the program allowing a simple variable to be
> undefined (i.e. no ud chain can reach from a reference to a
> declaration with no initialization). This worked very well
> in CDL in practice (CDL = Koster's Compiler Definition
> Language).

I presume that Ada 95 compilers that try to properly avoid unpredictable
behavior when an uninitialized variable is used do this kind of
tracking to determine whether the variable *might* be uninitialized,
and hence might be outside its declared range. 
Both GNAT and AdaMagic-based Ada 95 compilers seem to produce
"uninitialized variable" warnings these days.  At least in
the AdaMagic-based compilers, that information is used to
"bound" possible errors associated with using uninitialized variables, 
to avoid the dreaded erroneous/nose-demon situation.
 
-- 
-Tucker Taft   stt@averstar.com   http://www.averstar.com/~stt/
Technical Director, Distributed IT Solutions  (www.averstar.com/tools)
AverStar (formerly Intermetrics, Inc.)   Burlington, MA  USA