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From: dewar@gnat.com (Robert Dewar)
Newsgroups: comp.lang.ada
Subject: Re: Discriminated record question
Date: 8 May 2002 19:56:55 -0700
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Mark.Doherty@uk.thalesgroup.com (Mark Doherty) wrote in message news:<2d87db3f.0205080210.34726bf3@posting.google.com>...

> Does the compiler have the freedom to raise it as a 
> Constraint_Error?

Highly dubious if you ask me. Report it as a bug.

Note that GNAT is so kind as to give you a warning if
you declare a type like this:

     1. package q is
     2.    type x (a : natural := 0) is record
     3.       s : string (1 .. a);
                               |
        >>> warning: creation of object of this 
            type may raise Storage_Error

     4.    end record;
     5.
     6.    ss : x;
           |
        >>> warning: Storage_Error will be raised at 
            at run-time

     7. end;

And sure enough, if you run this program, Storage_Error
will be raised. I really think raising Constraint_Error
is very dubious here. What is likely going on is that
the compiler is getting an overflow trying to compute
the maximum size of the object. As I said earlier, I 
would report it as a bug.

The warnings in GNAT are quite useful (checkout the -gnatw
flag for turning them on, at the very least -gnatwu should
be used pretty much all the time, the only reason it is not
the default is that making it the default would require the
modification of literally hundreds of tests in our test
suite :-)

Robert Dewar
Ada Core Technologies