RE: Benefits of Sub-procedures -- RPG400-L

If I can add my 2p to this.. 

One thing that we have noticed is that when developing using subprocedures
you end up with a lot less bugs coming out in testing. My feeling is that
this is because you are coding smaller discrete blocks of code to perform
simple functions. It is protected from the rest of the program by having
local scope so no other section can inadvertently change it's data...

.. and to reiterate the point others have made about modules - we do not
allow modules to be re-used in more than one program or service program
object. 

Stu

PS. Having done your ILE course a few years ago Brian, it is still the
single best technical course I have ever been on. 

-----Original Message-----
From: Brian Parkins [mailto:PARKIB@xxxxxxxxxx] 
Sent: Thursday 23 October 2003 16:15
To: RPG programming on the AS400 / iSeries
Subject: RE: Benefits of Sub-procedures






I get asked this question all the time by students on my ILE courses.

My take on this is that (static) procedure calls do _not_ replace
(dynamic)
program calls - they _complement_ them.

The Dynamic Call (CALL and CALLP/EXTPGM) we've used since the S/38 is in
fact a WONDERFUL facility.  The late bind provides simplicity and
flexibility - with a relatively small performance overhead.  So, program
calls are A Good Thing - just as valuable as they ever have been.

On the other hand, Subprocedures provide a much better alternative to
Subroutines.  Many of the advantages have already been highlighted, (local
variables, parameter passing, automatic storage allocation + recursion,
more rigorous call interface, expression call, etc.).

To my mind, the big advantage of Subprocedures is the ability to "share"
code, (through a Service Program).

A Subroutine can be shared (proliferated) through the use of /COPY - but
results in a significant maintenance burden.  In contrast, a Subprocedure
can be packaged into Service Programs and shared in a similar manner to a
program object.  Service Programs act as a "function repository" - a means
of building and sharing your own built-in functions without the
proliferation problems of /COPY.

Now, if Subroutines (and /COPY) are _not_ used in an organisation, the
argument for the modularity/reuse which ILE supports becomes a little more
difficult.

Hope this helps.

Brian Parkins

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