Object oriented RPG

[Colin Williams <Williamsc@xxxxxxxxxxxxxxxxx>]

Now that sounds cool!

>-----Original Message-----
>From: boldt@ca.ibm.com [mailto:boldt@ca.ibm.com]
>Sent: Monday, December 06, 1999 1:54 PM
>To: RPG400-L@midrange.com
>Subject: RE: Runtime KLIST change?
>
>
>
>
>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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