Re: Is this expected behavior or not

["Randy Brukardt" <randy@rrsoftware.com>]

"Shark8" <onewingedshark@gmail.com> wrote in message 
news:87ec4b1d-f7cd-49a4-8cff-d44aeb76a1ad@googlegroups.com...
...
> Hm, true; speaking of object-attributes I sometimes [though not too often] 
> wish I could write something like:
> Procedure X( Input : Some_Type ) is
>  Temp : Input'Type := Some_Value;
> begin
>  -- Whatever needs done.
> end X;
>
> Is there any reason that should be disallowed / would be difficult for 
> compiler-writers to implement?

I've occassionally had such a thought, too. Probably the reason this doesn't 
exist is that Ada 83 didn't have type-valued attributes and thus it wasn't 
considered there. ('Base could only be used as an attribute prefix in Ada 
83). There would potentially be a cost to an object attribute vs. using the 
subtype name directly, in that the prefix would have to be evaluated (which, 
if it included function calls or checks, would generate some code).

I suppose there might be a problem in that this would provide a way to give 
a name to anonymous types. Most of the Ada rules presume that such types 
can't be named and thus can't be used in contexts where a name is required 
(like explicit type conversions). So there might be some problems raised by 
that; probably not insurmountable but makes it harder than trivial (in which 
case all of the trade-offs have to be considered - and given that the new 
capability here is either low or not desired - depending on your point of 
view - that makes it unlikely).

What I'm talking about is something like:

   procedure P (A : access Int) is
      Obj : A'Type; -- A second object of a single anonymous type, not 
possible now.
   begin
      Obj := A'Type(Some_Ptr); -- An explicit conversion to an anonymous 
access type, not possible now.
   end P;

It's not clear that there is any problem here, it's just that we haven't 
considered it and usually that means there is a problem there. :-) Could 
just be FUD, too.

                                              Randy.