Re: How to return an empty aggregate

[george.priv@gmail.com]

On Apr 6, 4:04 pm, Maciej Sobczak <see.my.homep...@gmail.com> wrote:
> On 6 Kwi, 09:00, george.p...@gmail.com wrote:
>
> > You receive the events for logging but you don't want
> > 5,000,000 records of the same to go in when some device malfunctions.
> > You rather want first 10, and something stating that this is serious
> > condition, etc. Is there a way to use stateless adapter or you have to
> > have a context?
>
> There is a way to have a filter Log that feeds its selected output
> into another Log'Class - and that second Log object can be whatever,
> including empty null log.
>
> Hint: essentially you want some Ada equivalent of the following pipe
> construct:
>
> $ someprogram | head > somefile.log
>
> which in some particular case might become just:
>
> $ someprogram | head > /dev/null
>
> as opposed to direct:
>
> $ someprogram > somefile.log
>
> or:
>
> $ someprogram > /dev/null
>
> The presence of "head" filter changes nothing in the applicability of /
> dev/null - that's why, in Ada terms, it can always have the same
> implementation:
>
> type Null_Log is new Log with null record.
>
> --
> Maciej Sobczak *www.msobczak.com*www.inspirel.com

I think you misunderstand.  I am not questioning value of the concept
of adapter in general.  My point was that value of adapter (strategy
if you wish) with no context is approaching 0 and my example was to
demonstrate precisely that point.

G.