Re: Interresting, possibly buggy behavior in GNAT generics w/ expression function.

[Bill Findlay <yaldnif.w@blueyonder.co.uk>]

On 29/03/2013 14:54, in article
615039cc-f33b-486a-b242-2c87292271d6@googlegroups.com, "Shark8"
<onewingedshark@gmail.com> wrote:

> On Friday, March 29, 2013 8:47:36 AM UTC-6, Simon Wright wrote:
>> Shark8 <onewingedshark@gmail.com> writes:
>> 
>> 
>> 
>>>     Function Image(Value : Positive) Return String is
>> 
>>>       ( --if Value not in positive then "" else
>> 
>>>         Units.Constant_Reference( Attribute_Units, Value ) );
>> 
>> 
>> 
>> Or, of course, Attribute_Units (Value) !
> 
> That doesn't work.
> That I'm pretty sure is a bug; in any case at least the [compile-time] error
> it gives is utterly useless:
> generic_attribute_set.ads:36:07: "" is undefined

Type resolution in conditional expressions by GNAT GPL 2012 is not all it
should be.  E.g. I had to make the second 0 into a qualified expression in:

   function XR (X : M.i04)
   return M.i64 is
   begin
      return (if X = 0 then M.i64'(0) else GR(X));
   end XR;

because GNAT could not otherwise deduce its intended type, even though GR(X)
is of type M.i64.

Further to bijou buglettes in Ada 2012 mode, I had to write this:

    for s in slice'Range loop
    exit when slice(s) = all_blanks_code;
       h := rotate_left(h, 2) + slice(s);
    end loop;
    
To avoid this:

    for s of slice loop
    exit when s = all_blanks_code;
              |
>>> warning: variable "s" is not modified in loop body
>>> warning: possible infinite loop

       h := rotate_left(h, 2) + s;
    end loop;

-- 
Bill Findlay
with blueyonder.co.uk;
use  surname & forename;