Re: Additional RPGLE Enhancement Requests

Charlie Massoglia, Massoglia Technical Consulting, Inc. wrote:
> Hans Boldt wrote:
>
> >The reason I mentioned the idea of relaxed OVERLAY rules is that the
> >combination of relaxed OVERLAY rules and OVERLAY(x:*NEXT) should go a
> >long way in avoiding database dependencies.  Consider the following
> >data structure:
> >
> >   D  Combined     DS
> >   D   Field1                 OVERLAY(Combined:1)
> >   D   Field2                 OVERLAY(Combined:*NEXT)
> >   D   Field3                 OVERLAY(Combined:*NEXT)
> >
> >The data structure name COMBINED is implicitly defined with a length
> >that is the sum of the subfield lengths!
> >
>
> This is fine except Combined must be a data structure.  It can not be a data
> structure subfield.

Well, I knew you were going to say that!  That's what prompted the
following idea.

>
> >I just had another wild and crazy idea:  How about if we implicitly
> >define overlayed subfields with the appropriate length to contain all
> >overlaying subfields?  (I'm not sure if I can convince the rest of my
> >team on this one, though!)
> >
> Hans, could you please explain this further, perhaps with a sample.  I'm not
> sure what you mean.

As I said, this is just some random bit of brainstorming, so I don't
know all of the ramifications yet.  But here is an example:

   D DataStruct    DS
   D   Combined
   D     Field1                 OVERLAY(Combined:1)
   D     Field2                 OVERLAY(Combined:*NEXT)
   D     Field3                 OVERLAY(Combined:*NEXT)

As you know, a data structure without an explicit length specified is
implicitly defined big enough to hold all of its subfields.  What I am
proposing is that we have the same rule for subfields.  If a subfield
is not otherwise explicitly defined and the subfield has subfields
OVERLAYed on it, the subfield is implicitly defined as character with
a length big enough to hold all of its OVERLAYing subfields.

So, in this example, if FIELD1, FIELD2, and FIELD3 are each 10 byte
long fields, subfield COMBINED is implicitly defined as 30A.  If the
definition of any subfield changes, the definition of COMBINED would
also change on recompile with no source change.

This shouldn't be too difficult for us to implement since we already
have to deal with computing the length of data structures like this.

Cheers!  Hans

Hans Boldt, ILE RPG Development, IBM Toronto Lab, hboldt@vnet.ibm.com

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