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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Interresting,
 possibly buggy behavior in GNAT generics w/ expression function.
Date: Mon, 1 Apr 2013 19:46:06 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2013-04-01T19:46:06-05:00
List-Id: <comp.lang.ada>

"Adam Beneschan" <adam@irvine.com> wrote in message 
news:65330bfe-39e4-4f7b-85f5-e06e9458bf29@googlegroups.com...
On Friday, March 29, 2013 6:04:28 PM UTC-7, Randy Brukardt wrote:

...
>Randy, it looks to me that the original code called Image(...) only from 
>inside the
>generic specification or body, not outside.

OK, I didn't see that, because the OP I got only had a description of the 
spec in it, no code at all.

>I'm sure Randy already knows this, but for the benefit of anyone who 
>doesn't: When
>a call to Image occurs inside the generic spec or body, the meaning of 
>Image (i.e.
>which one is selected) depends only on the stuff the compiler knows when 
>the
>generic is *compiled*; the actual types used in an *instantiation* don't 
>matter,
>for this purpose.  (Yes, I know things might be a bit more complicated when
>dispatching is involved, but that's not an issue here.)  For compilers that 
>use
>"macro expansion" to implement generic instantiations (including GNAT, but 
>not
>Janus/Ada), this poses challenges for the compiler writer, because it 
>doesn't work
>to simply replace Attribute_Values with Integer when recompiling the 
>generic.  This
>looks like a case that fell through the cracks in GNAT.

Right. Calls in the body *always* should treat Attr_Value and 
Natural/Positive as different types; the actuals don't matter. So if 
changing the subtypes is changing the called routines, you have a GNAT bug, 
pure and simple.

                                       Randy.