[Coco] Portal-9 info

[Roger Taylor]

I've been in touch with the author of HLA about my techniques for handling 
object-oriented programming in assembly, and much to my surprise, he 
totally agreed with several things I am doing from the assembler to help 
support this type of concept.  It's really just basic stuff to most people, 
but I have never done structure support in assembly, so I had some 
questions to him about my approach on things.

CCASM allows structures to be created where you can later access the fields as:
1) direct addresses
2) offsets

shape   struct
width   rmb     2
height  rmb     2
         endstruct

This creates a simple data structure.  It sort of mimicks the namespace 
directive in that you can access the fields by using:
ldd     shape.width
or
ldd     shape.height

Only, CCASM uses : instead of . for the separator.

If you have copies of the structures in memory, or objects, you can access 
the same fields using the indexed instructions, like:

ldu     object1
ldx     {shape}:width,u
ldy     {shape}:height,u

ldu     object2
ldx     {shape}:width,u
ldy     {shape}:height,u

Ofcourse, the above is not even close to being what I would call real 
OOP.  When I started on the object-oriented programming stuff and allowed 
Classes to be created, I basically just added some more fields above the 
data fields, which are pointers to procedures and methods for that 
object.  I am now updating CCASM to automatically allow a structure to be 
created based on another structure type, like:

circle  struct  shape
box     struct  shape

This will clone the original structure and give the same fields to the new 
type, whether it's a simple data type or a Class type.

This is leading up to a "class" psuedo-op which is on the way.  It will 
work just like struct only it will do some automatic stuff that currently 
is being done by brute force in my OOP example.

This is getting fun and I am already creating classes you'll be able to 
include into your programs like:
         include graphics_class.asm (invoke any mode, clear screen, plot 
pixels, peek @ pixels, draw objects, etc.)
         stdio_class.asm (keyboard, serial, joystick?)
         console_class.asm (printing to the text screens, etc)

With these and CCASM's upcoming "call" command which pushes it's parameters 
to the stack before calling the address, good things are on the way.

It just keeps getting easier and easier to write assembly language programs.

----------
Roger Taylor


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