Re: Elaboration order handling (Was: Bug in 'gnatmake')

[Robert A Duff <bobduff@shell01.TheWorld.com>]

Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org> writes:

> On 06/21/2013 01:43 PM, Adam Beneschan wrote:
>> Well, it could have, prior to Ada 2005.  That's no longer possible, because
>> of null procedures.
>
> Ah, yes, another unnecessary shortcut.

It is important to the way interfaces work that procedures can be known
to do nothing on their SPEC.  I suppose it would be possible to allow
"is begin null; end;" on the spec, but that would be more complicated
-- requires either special syntax rules, or special semantic rules.

So "is null;" makes sense for that.

It is also useful for optimization purposes for procedures to be
known to do nothing.  E.g. Finalize defaults to doing nothing,
so a type that does not override Finalize can be optimized to avoid
finalization overhead, without looking at bodies of non-visible things.

> I addressed this in detail in a reply to Duff. Basically, I find it hard
> to find a specific declaration when reading such languages.

It takes some getting used to, but I don't find it onerous.  You already
need to search for things in Ada as it is -- the declaration could be in
some outer block or procedure or parent package or some use-claused
package.

And in some cases, it makes it EASIER to find the declaration, because it
comes just before.  Compare:

        X, Y : T;
        Init (X, Y);
        ... -- 100 lines
    begin

versus:

        X, Y : T;
        ... -- 100 lines
    begin
        Init (X, Y); -- far away from X and Y

- Bob