Re: Porting to Ada 9x

Re: Porting to Ada 9x

[Tucker Taft]

In article <1993Jul29.134804.17614@aio.jsc.nasa.gov> 
  ddanley@gothamcity.jsc.nasa.gov writes:

>In the Ada 9x compatability guide, Bill Taylor stated that there 
>are 32 upward incompatabilities between Ada 83 and Ada 9x.  
>Are there only 32 upward incompatabilities to the 9x specification?

Actually, the number of upward incompatibilities has dropped since
Bill Taylor's initial report was released.  In any case, almost
all of the incompatibilities are straightforward to accommodate, as the
compiler detects them or can warn the programmer of them, and
the fix is relatively mechanical (e.g. add an underscore to
the end of an variable name that is now a reserved word).

There are a few incompatibilities that are a bit 
more difficult -- for example, the number of characters
in Standard.Character has gone from 128 to 256.  This changes the
value of Character'Last, and means that the programmer has to
decide how they want to handle 8-bit characters as opposed to
Ada 83's 7-bit characters.  To ease transition, this change has
been approved for Ada 83 compilers, so compilers can start supporting
the 8-bit character model, and programmers can get a jump on handling
8-bit characters properly.  It is also anticipated that Ada 9X compilers
will warn users during the transition period when they encounter
references to values such as Character'Last that have changed.

S. Tucker Taft     stt@inmet.com
Ada 9X Mapping/Revision Team
Intermetrics, Inc.
Cambridge, MA  02138