RE: ARGH!!! (was file open with LR)

["Joe Pluta" <joepluta@xxxxxxxxxxxxxxxxx>]

> From: Buck
> 
> > Joe, doesn't one lose the value of reusable code
> > if you can not depend upon it?
> 
> Great question!  I have strong feelings on this matter so indulge me
for a
> moment.

I avoided this conversation because it's highly opinion-oriented, but I
have to at least say my piece here.

Reusable code is as close to "the grail" as we can get.  The problems
that occur are not because the code is reusable, but because they're
(re)used incorrectly.

This is the concept of the "side effect", which is what OO is all about
(removing side effects, accessing logic only through interfaces).  In
Brad's case, there was a horrible side effect of calling the program:
namely the file was left open in the default activation group (as close
as I can figure from his posts).  This side effect was not documented,
and in fact probably wasn't even considered by the folks who wrote it,
because they didn't think about it.

If you write a file I/O routine, you better be damned sure that everyone
who uses it understands the ramifications.  Does it open files?  Share
them?  Position them?  Expect the position to stay the same?  Typically,
if you write a file I/O routine, you should probably ensure that you
have your own ODP.  This would alleviate any side effects such as the
one Brad is seeing.  You can do this relatively easily by having an
initialization routine that overrides the file with a SECURE(*YES) and
SHARE(*NO) and then opens the file.  If your program, however, counts on
the RPG cycle to open the files, then you need to make sure anyone
calling this knows it.

This problem was NOT a failure of the architecture of reusable code, it
was simply a failure of IMPLEMENTING a reusable object, and specifically
of side effects which were not documented and thus not known.  This, by
the way, is another reason that I advocate moving ALL file I/O for a
file into a single module; it avoids some of these issues.  It sometimes
causes a little extra upfront work, but in the end it makes your life a
lot cleaner.

Anywho, don't want to step on toes here, I just want to chime in with my
opinion that the issue was NOT the reusable code at fault - it was the
undocumented side effects which burned Brad's butt.

Joe