OO in RPG -- RPG400-L

>> Does anyone have any ideas (Brad Stone, Joe Pulta, Hans
>> Boldt) how to write
>> RPG code in a way that simulates an Object Orientated approach?

Well Alistair even though I am not listed in your list of luminaries I
do have an idea for you... It is one that I am considering myself.
Back in the good ole days of C++ before there were any C++ compilers
there was a pre-processor called CFRONT. This would take the C++ code
and then pre-process it and make C code. The same methodology could be
applied to RPG... I too would love if some OO extensions were added to
RPG mainly because I am often explicitly enjoined by my client that I
will ONLY WRITE in RPG...  No choices of which hammer to drive the
screw with :-)

So you may want to see if you can get ahold of the CFRONT source code
and if you understand C and C++ that should give you some great and
proven ideas on how to do what you want. Oh and if you decide to wait
on me... Well I have about a zillion projects that have nearly the
same priority and fun factor so I do not know if or when I will get
around to looking at this closer. :-)

One of the big things about OO for me is encapsulation, C++ does this
by having an implicit *this pointer contained in every object and
every object method takes *this as a parameter so that it knows which
instance of the object to work on. This could be simulated manually
without too much trouble by adding a pointer as the first parameter of
your object methods.

For example, make a service program that contains a few methods...
New which returns a pointer to the storage on the heap for a newly
created instance of an object.
Free which takes as it's only argument the pointer to an object
instance that you want to release from memory.

Then perhaps some functions like IsNull which would take one pointer
and return a boolean (indicator). Oh and Hans, would it be hard to
make a synonym for *On as a symbolic constant... *True? I know I know
I can add True as a constant (which is what I do) but it would be more
clear for me if *True were used rather than *On (Both meaning the same
thing of course). *False = *Off naturally being in the same request.

Then you could make some functions that take 2 pointers as input for
boolean and assignment operations... IsEqual, IsGreater, IsLesser,
Assign...

Last after you have all your "object" functions determined count up
the pointer parameters (of which basically all your parameters will
have to be defined so that you can override what in the world they
are). and create a dispatch function.... Until we can qualify what
service program procedure we want to invoke ServicePgm.Method you will
have to lose type checking so that you can do what you want... Either
that or Wart everything with the object name as a prefix/suffix...
Both being quite ugly :-) With the dispatch function you would name it
by the object name...

CallP Customer('New' : NewCustPtr) for example...

Hope that helps
Eric

----------------------------------
Eric N. Wilson
President
Doulos Software and Computer Services


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