Re: Real syntax problems in Ada

[Adam Beneschan <adam@irvine.com>]

On Tuesday, August 28, 2012 2:25:09 PM UTC-7, Shark8 wrote:
> On Tuesday, August 28, 2012 3:07:32 PM UTC-6, Adam Beneschan wrote:
> 
> > On Tuesday, August 28, 2012 1:53:01 PM UTC-7, Shark8 wrote:
> 
> > 
> 
> > In the past, I've wanted something like (null array), which would be consistent since Ada already has (null record).  The language would have to define what the actual bounds of the array are, however, since a program can still refer to A'First or A'Last and they have to be defined to be something.  Starting with Ada 2005, it's now possible to say (1..0 => <>), which makes things better than they were before--at least there's no more problem of having to come up with a dummy value to put on the right side of the arrow.
> 
> 
> 
> Except in the case of an array of not null access values. :(
> 
> (At least w/ GNAT; it rejects <> because the default is null, which is excluded.)

Hmmm... I can't even get GNAT to display a warning.  I'm using 4.5.2.

Anyway, the behavior seems wrong; I can't find any Legality Rule that makes it illegal to declare an uninitialized object of any kind whose type is null-excluding access.  Of course it will raise Constraint_Error at runtime, although it won't in a (1..0 => <>) case since the program doesn't attempt to initialize any values.  I'm sure GNAT has a nonstandard mode that will reject a program if it "knows" there is something that is sure to raise an exception like this, but it shouldn't be doing it here.

                     -- Adam