Re: Refactoring and Ada

[Richard Riehle <richard@adaworks.com>]

Larry Kilgallen wrote:

> > What happens when you read junk off the interface?
>
> Doesn't 'Valid detect that ?

It turns out that 'Valid is not as useful as many of us thought it was. For
example,  the result of an erroneous result from unchecked conversion,
which we originally thought was harmless if we checked it ourselves
with 'Valid before using it is a problem.   Consider the following,

               type X is ... ;
               type Y is ... ;

               function Convert is new Ada.Unchecked_Conversion
                                         (Source => Y, Target => X);


                X := Convert (Y);     -- suppose X is erroneous or not valid
                if X'Valid then ...      -- We used to think this was OK.
                                                 -- Some compilers fail on this because of an
interpretation
                                                 -- of the ALRM rules.

 At present, one must wonder about the usefulness of 'Valid.

Richard Riehle