Re: How to return an empty aggregate

[Maciej Sobczak <see.my.homepage@gmail.com>]

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