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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Suggestion for gnatstub
Date: Mon, 11 Nov 2002 14:32:35 -0600
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Date: 2002-11-11T14:32:35-06:00
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Robert A Duff wrote in message ...
>"Marin David Condic" <mcondic.auntie.spam@acm.org> writes:
>
>> I can't think of too many other reasons to write a null procedure. If
it was
>> going to stay null forever, then why have it at all. Seems like the
>> mechanism is there so you can have a procedure waiting for the
programmer to
>> find the elusive Round Tuit. :-)
>
>I can't think of "too many", either, but I can think of some.  Just the
>other day I wrote a generic procedure to walk a tree.  The generic
takes
>two generic formal procedures, Pre_Action and Post_Action, which are
>called during the tree at the points you would guess.  They have
>defaults, "is Do_Nothing", so you can specify one or the other.
>Guess what procedure Do_Nothing looks like.  ;-)


Most action routines (callbacks) in Claw are defined as procedure
When_something (...) is null; end When_something;
These may be overridden in for a derived type, but the original routine
is likely to remain with a null body forever. I believe this is common
in object-oriented code.

            Randy.