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GKern@xxxxxxxxxxxxxxxx wrote:
I've seen a few instances of where the actual code for a prototype (or
more than one prototype) is found at the bottom of an RPG source member.
I think you're confusing the terms "prototype" and "procedure". The
prototype is the part in the D-specs that must be included in the module
that uses the CALLP opcode. It can be included by /copy, and often is
as Matt has described. Prototypes can be used to call both procedures
_and_ programs. The main purpose of the prototype is to allow the
compiler to do magic like warning you about parameter mismatches and
automatically doing type conversion for you (eg. packed to zoned,
character to varying character, ...).
The procedure what contains the actual code, the part you are seeing at
the bottom of the RPG source.
The only reason I see for doing this would be to be able to use them like
subroutines that could accept parameters where the process is performed
only within a single program. But then wouldn't that still lend itself to
a /copy book?
Yes. If you are familiar with Java or other OO languages, this is like
a "private" method. You essentially get a subroutine that can avoid
using global variables and has a well defined interface. One benefit is
that if you later realize that this is something that could be used in
multiple programs after all, it is a lot easier to move it to a service
program than if it was originally written as a subroutine.
The fact that procedures can be (and should be, where possible) written
so they have no side effects leads to IMO the biggest benefit of
procedures over subroutines. Maintenance is a lot simpler if you can
just look at the CALLP line and determine whether the variables you are
interested in are used or changed by the procedure. With subroutines,
you have look at the subroutine code and determine which variables are
updated and which key lists are used before you can confidently change
any of the code surrounding the EXSR.
Also, just to be clear, it would be the prototype in the copybook, not
the procedure. Your instinct is right however. If the code is reusable
within a single program, there is a good chance it can be reused in
other programs as well.
HTH,
Adam
midrange.com
