Re: [BLACKBOX] Variant Records vs. Component Pascal

From: [at]} <Chris>
Date: Fri, 1 Jan 2010 09:17:03 +1030

----boundary-LibPST-iamunique-681082525_-_-
Content-type: text/plain

Welcome! I think you'll find many here with similar backgrounds and
interests. My language path started in the late 60's with assembler, ALGOL
and FORTRAN IV, followed by Pascal in the 70's, Modula-2 in the 80's and
Delphi and Oberon / CP in the 90's. C was also somewhere in there for about
10 years but I've mostly been able to suppress those unpleasant memories ;-)

I'm sure you will be able to do what you are trying to do but recall similar
difficulties with variant records vs. type extensions when first using
Oberon. One brilliant book that really helped me make the switch to the
Oberon style of programming is Hanspeter Mössenböck's "Object-Oriented
Programming in Oberon-2". While reading that I had that satisfying "now I
get it!" experience. Unfortunately it is not easy to get a copy these days.

As to your specific current task - I'm sure somebody else will show you how
to do it once they've all recovered from the New Year celebrations.
Otherwise I'll try and track down some helpful examples for you.

Wishing you and everybody else here a Happy and Peaceful New Year,

Chris Burrows
CFB Software
http://www.armaide.com

________________________________

        From: BlackBox [mailto:BLACKBOX{([at]})nowhere.xy
Stephen R. Troy
        Sent: Friday, 1 January 2010 7:42 AM
        To: BLACKBOX{([at]})nowhere.xy
        Subject: [BLACKBOX] Variant Records vs. Component Pascal
        
        
                Hello List,
        This is my first post to this list. To help you reply, I started
programming digital computers, in machine language, in 1957. Since then I
have done scientific and engineering programming in FORTRAN, BASIC, Pascal,
and then Modula-2 for many years. I have only limited familiarity with C.
Now retired, recently I have moved to Oberon and now Component Pascal,
writing programs to support hobbies.

        I have a program I have been evolving for several years, which reads
in a database which is in a structured ASCII text file using a third-party
database schema. The program develops several index files, performs various
sorting and filtering operations on these indexes, and the uses the modified
indexes to write out reports using the same database schema. There are
three main types of records, and I was able to write very efficient sorting
and filtering procedures in Modula-2 by writing the records as variant
records of a basic type, then instantiating the records by pointers. My
indexes were linked lists of the pointers, both linear and binary trees, and
so I could find, sort, and filter each of the three types of records using
the same very efficient code, because I manipulated only the pointers'
"next-record" pointer in the linked lists, not moving any records in memory.


        But I apparently I can't use this method in Component Pascal because
variant records are not allowed. I tried defining a basic record as an
ABSTRACT type, then defining each of my three record types as extensions.
However, I can't instantiate a record as a NEW(pointer to basic type), and I
can't use a single sort routine with each of the three (pointer to extension
type) -- I need three separate routines, which is clumsy at best, and seems
contrary to the basic intent of Component Pascal. I tried defining the
basic record type as EXTENSIBLE, but that made no difference. I found an
obscure section in the Component Pascal documentation that said that using a
RECORD [union] system flag, which allowed a "C-type" union data structure,
it was possible to simulate Pascal- and Modula-style variant records, but
the example in the documentation will not compile -- it gives an "invalid
system flag" error message on the [union] flag.

        Any suggestions would be welcome at this point.
        Thanks,
        Steve Troy
        
        ---- To unsubscribe, send a message with body "SIGNOFF BLACKBOX" to
LISTSERV{([at]})nowhere.xy

----
To unsubscribe, send a message with body "SIGNOFF BLACKBOX" to LISTSERV{([at]})nowhere.xy----boundary-LibPST-iamunique-681082525_-_-
Content-type: application/rtf
Content-transfer-encoding: base64
Content-Disposition: attachment; filename="rtf-body.rtf"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----boundary-LibPST-iamunique-681082525_-_---

Received on Thu Dec 31 2009 - 23:47:03 UTC