Re: Suggested Technique

[rob@xxxxxxxxx]

The logic is that you shouldn't have multiple exits out of a loop of this 
nature.  To some, that's an edict from God.  Granted, without the leave 
your loop (as presented) would be infinite therefore there would never be 
an exit on the enddo.
The argument is that you may have more conditions than F3 to exit.  Like a 
system shutdown detected or any other number of animals.  Then you would 
have something like:

ChuckIt=*off;
Do until ChuckIt;
...
Select;
When Fkey=F3;
  ChuckIt=*on;
When ThisSituation;
  // don't really do anything, but don't set ChuckIt.  Sort of like an 
iter.
...
When Shutdown;
  ChuckIt=*on;
EndSl;
EndDo;

The problem is that if you like to write huge monolithic code then it gets 
complicated keeping track of whether or not you turned ChuckIt on.

I used to follow this mantra, but it does tend to get rather complicated 
at times.

I could go either way on this.  Just summing up the arguments.

Rob Berendt
-- 
Group Dekko Services, LLC
Dept 01.073
PO Box 2000
Dock 108
6928N 400E
Kendallville, IN 46755
http://www.dekko.com





"Larry" <Larry_Ducie@xxxxxxxxxxx> 
Sent by: rpg400-l-bounces@xxxxxxxxxxxx
01/31/2005 03:58 PM
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RPG programming on the AS400 / iSeries <rpg400-l@xxxxxxxxxxxx>


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Re: Suggested Technique






Hi Alan,
 
<snip>
There are some brilliant programmers here, however, who advocate avoiding
use of the "iter" and "leave" op-codes. I find it hard to avoid using them
myself, but am still open on that issue.
</snip>
 
Now there's a statement! :-)
 
I would be VERY interested to hear the reasons why LEAVE and ITER have
entered the "Hall of Shame" along with CABxx and GOTO.
 
Personally, I find them very useful and would need a very, very hard sell 
to
convince me to stop using them. They do not preclude well structured code,
they have definite branching end-points, and they do not make code less
readable to a developer: All long-standing accusations levelled at CABxx 
and
GOTO.
 
For example - a classic screen loop:
 
// Display screen...
do *hival 
 
exfmt screen
 
// If user presses F3, leave screen loop...
if F3_pressed
leave
endif
 
// Validate user input...
validateInput()
 
// If user enters invalid data, re-display screen, displaying error
message...
if userEntersInvalidData
iter
endif
 
// If user elects to update current valid data, update and leave screen...
if F8_update
updateData()
leave
endif
 
enddo
 
 
For me this code is simple - you can only leave the screen if you press F3
or update valid data. How do I know??? There's only two ways to leave the
screen - via the two LEAVE op-codes. If the code goes beyond the enddo 
then
F3 or F8 MUST have been pressed. In the case of F8, valid data MUST have
been entered. If the user enters invalid data then I force a re-display of
the screen (ITER) before any update code is reached - this forms a nice 
code
buffer, beyond which I am assured that the input data is valid.
 
I also prefer using "do *hival" because I do not want any "implicit" exits
of the loop. I want to see the exit strategy EXPLICITLY coded within the
screen loop. My time is more precious than the CPU cycle time. If I can
read/modify the code faster because there are large marker flags in front 
of
me then my company saves money. It's the old adage - KISS! 
 
Just my preference.
 
Cheers
 
Larry Ducie
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