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From: george.priv@gmail.com
Newsgroups: comp.lang.ada
Subject: Re: How to return an empty aggregate
Date: Sat, 5 Apr 2008 15:36:36 -0700 (PDT)
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Date: 2008-04-05T15:36:36-07:00
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On Apr 5, 5:14 pm, Maciej Sobczak <see.my.homep...@gmail.com> wrote:
> On 5 Kwi, 18:04, george.p...@gmail.com wrote:
>
> > Can you provide non-academic example?
>
> For the empty record?
> I thought I did already. :-)
> This might be a challenge, because we have no judge that can say
> whether something is academic or not.
>
> Consider a logging system that is designed with OO in mind. There is a
> base interface with some operation(s) for logging and a bunch of
> concrete implementations for various log destinations - one for disk
> file, one for network output, one for database persistency, etc. The
> part of the program that does something useful takes Log'Class and
> feeds its log entries via given Log'Class parameter to whatever
> happens to be a concrete Log implementation - a classic strategy
> pattern.
>
> What would you do to... switch the logging off?
>
> I would create the derived (concrete) log that is *empty* and does
> nothing and pass it as Log'Class to wherever it is expected.
> It cannot be simpler than that.

So you derive concrete from not-empty type?

>
> Is it academic? I would do it at the nearest opportunity.
>
> --
> Maciej Sobczak *www.msobczak.com*www.inspirel.com