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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Is this expected behavior or not
Date: Thu, 14 Mar 2013 17:01:03 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2013-03-14T17:01:03-05:00
List-Id: <comp.lang.ada>

"Shark8" <onewingedshark@gmail.com> wrote in message 
news:99929f93-b80f-47c3-8a37-c81002733754@googlegroups.com...
> On Wednesday, March 13, 2013 3:09:24 PM UTC-6, Randy Brukardt wrote:
...
>> The not-defined procedure 'Succ would have been much more useful because 
>> it
>> could replace expressions like:
>>
>>     <Very_Long_Name> := <Very_Long_Name> + 1;
>> with
>>     <Very_Long_Name>'Succ;
>>
>> which would eliminate the potential for errors, possibly generate better
>> code (by not having to evaluate <Very_Long_Name> twice if it contains
>> function calls), and eliminate the hair-brained calls for ":=+" operators
>> (which don't even work for Ada).
>>
>
> Would there be a problem using this?
>
>    Generic
> Type T is (<>);
> with function Succ(Input : T) Return T is T'Succ;
>    package Test is
> -- Body does whatever is needed requiring Very_Long_Name as T.
>    end Test;

I don't see how this would work. You need to be able to use it on multiple 
<Very_Long_Name>s in order to make it worth the effort.

Something like:

    generic
        type T is (<>);
    procedure Succ (Obj : in out T; Count : in Natural := 1) is -- Note: I 
know this requires a separate spec!
    begin
          for I in 1 .. Count loop
              Obj := T'Succ(Obj);
          end loop;
    end Succ;

would match the intended attribute semantically.

But it doesn't help much, because you have to write the generic somewhere, 
and then you have to instantiate it when you need it as well. That's not 
very helpful for what is intended to be a short-cut (you usually would end 
up typing more). The big advantage of an object attribute (like this 'Succ 
or GNAT's 'Img) is that you don't have to figure out the nominal subtype of 
the object to increment it once (which you do to write an instance of my 
Succ generic).

                                         Randy.