RE: Runtime KLIST change?

[boldt@xxxxxxxxxx]

Alan wrote:
>>> Why, oh why, is RPG adopting pointers, the single greatest weak point
of
>>>C++
>
>Because there are certain classes of problems that cannot be solved
without
>them.
>
>A language like Java can get by without them because it is object oriented
>and, by building new classes, you can extend the language but somewhere
down
>in those classes somebody has to write in "C" or some other language with
>pointers. The java class just hides it.

I'd just like to add a couple of points.  Any modern language
that claims to not have pointers is simply playing games with
semantics.  Java doesn't have "pointers", but when you're
dealing with objects, you're really dealing with "references"
to objects.  Likewise in Perl, you don't have "pointers", you
have "references".  Same wine, new bottle, sort of.

>
>These are options that RPG ILE does not have so you have to have pointers.
I
>find to write many types of service programs, you just cannot get past
them.
>Any type of dynamic memory allocation (linked list, etc).
>
>Your message does point to the same fear I have. Pointers usage, in my
mind
>anyway, should always be encapsulated in a function and hidden. Using
>pointers in the general body of a program is scary to me and, of course,
>there is always that fear that someone will misuse a powerful tool.

Excellent point.  Pointers are a very low level concept in any
language.  (Pointers are the "goto" of data structures!)
Pointers are best used within a higher-level abstraction.  When
implementing some higher-level data structure, such as a linked
list or tree, the user of such a data structure shouldn't have
to know anything about how pointers work.

Here's an example:  You could have a service program that
implements a linked list.  One procedure would "create" the
linked list and return a "reference" (really a pointer) to the
data structure.  That reference would be passed by the user to
all other procedures within that service program.  The other
procedures would handle searching, insertion, iteration, and
deletion operations on one particular linked list.  In fact,
this is almost, sort of like object-oriented programming!

In practice, though, even if you take this style of object-
based design, the users of such a high-level data structure
really can't get away completely from understanding how
pointers work.  In this case for example, for the linked list
service program to be completely general, you'd have to deal
with references to the data in each node of the list.  This
would be fine if the data in each node were also some form of
high-level "object", but for standard RPG data types, you'd
need at least to define some based variables in your program.

(Actually, lately, I've been toying with the idea of how to
implement some form of real object-oriented programming in
RPG without having to add any language enhancements by
extending the approach described above.  Almost everything
could be handled relatively easily except for the
deallocation of object storage.)

Cheers!  Hans

Hans Boldt, ILE RPG Development, IBM Toronto Lab, boldt@ca.ibm.com


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