Re: how to let my program sleep a while -- RPG400-L

�
Hello Booth,

You wrote:
>As usual your suggestion is best. Much better. Two procedures it shall
>be. Now, (every body skips over the easy stuff!) why do I want to use

>"CallP Sleepfor('00:30:00')"

>instead of

>"Call 'SleepFor'"
>"Parm '00:30:00' Parm8 8"

Because CALLP requires a prototype which the compiler uses to verify that the
data type
specified on the prototype is compatible with the the type of data actually
used on the
call.

With CALLB (and indeed with CALL) the invoker can pass any old crap to the
procedure.
Prototypes help make robust software by catching stupid programmer errors**
during
compilation rather than run-time. It's not perfect but it a bloody sight
better than
the alternative.

Barbara's comment on the choice of names is correct (and in fact the choice of
name is
the single most important aspect of a procedure). In this case you have two
similar but
different procedures. They need different data types. sleepFor() needs a
duration but
sleepUntil() needs an absolute time. You should define the prototypes
accordingly e.g.,

D sleepUntil PR
D time T VALUE TIMFMT(*HMS)

such a prototype will stop the caller from passing character or numeric data
unless it
can be converted by the compiler into the correct type. Since RPG doesn't have
a
duration data type we need to content ourselves with a numeric value of some
sort e.g.,

D sleepFor PR
D duration 5I 0 VALUE

but at least that limits the possible sources of crap data. The onus is still
on the
programmer to pass the correct stuff but with prototypes you can restrict the
truly
creative. (You may decide to design sleepFor() to accept a time data type and
then
convert it to a duration -- you might choose to interpret the time as an offset
from
midnight and the procedure will sleep for that many hours, minutes, and
seconds.) In my
example from a few days ago I defined the parameter as a 6,0 packed field
because the
range of allowable values on DLYJOB is 1 to 999999.

Now see if you agree that the two procedures described above are better than
one like
the following:

D sleep PR
D delay 5I 0 CONST OPTIONS(*OMIT)
D resumeTime T CONST OPTIONS(*OMIT:*NOPASS)

I know a lot of this appears to be simply style but think about it for a bit --
and read
some stuff on Object Oriented (not Orientated!!) Design. Two good books on the
subject
are:
Designing Object Oriented Software by Rebecca Wirfs-Brock
Design Patterns by Erich Gamma et al.

These books should be on all programmer's bookshelves alongside the
well-thumbed
3-volume (unfinished) set by Donald Knuth.

Note that you may choose to create just such a sleep() procedure to do the real
work and
then wrap it in a facade using the first two prototypes. It depends on how
important
abstraction and encapsulation is to you. In this case sleep() would be private
while
sleepFor() and sleepUntil() would be part of the public interface.

>I understand that for most of you this is pretty basic, but hey, I just
>don't know the answer.

And now you do :)

** (i.e., those errors that are human mistakes rather than errors made by
stupid
programmers -- nothing shields you from those)

Regards,
Simon Coulter.

��������������������������������������������������������������������
�� FlyByNight Software AS/400 Technical Specialists ��
�� Eclipse the competition - run your business on an IBM AS/400. ��
�� ��
�� Phone: +61 3 9419 0175 Mobile: +61 0411 091 400 ��
�� Fax: +61 3 9419 0175 mailto: shc@flybynight.com.au ��
�� ��
�� Windoze should not be open at Warp speed. ��
��������������������������������������������������������������������
+---
| This is the RPG/400 Mailing List!
| To submit a new message, send your mail to RPG400-L@midrange.com.
| To subscribe to this list send email to RPG400-L-SUB@midrange.com.
| To unsubscribe from this list send email to RPG400-L-UNSUB@midrange.com.
| Questions should be directed to the list owner/operator: david@midrange.com
+---