[Oberon] FPGA - Pictures.Mod composition

[August Karlstrom]

On 2017-10-01 18:57, Tomas Kral wrote:
> Just realised when Pictures type is extended from Bitmaps,
> Bitmaps.New(P,..) needs to accept pointer to its `superclass',
> otherwise some type members are duplicated. Correct???
> 
> I need to to be also explained, what we call `superclass',
> `baseclass' in Oberon terminology.
> 
> Order of type extension:
> T1 -> T2 (T1) -> T3 (T2).. Tn(Tm)
> 
> Order of type creation:
> M1.New(T2,..) <- M2.New(T3,..) <- .. Mn.New(Tm,..)
> 
> For the reason above I use two New procedures in Bitmaps:
> 
> PROCEDURE Bitmaps.New(w, h, dpt) : Bitmaps;
> PROCEDURE Bitmaps.New2(B: Bitmap; w, h, dpt) : Bitmaps;
> 
> Is there a better recommended naming standard for this, than the above?

If I'm not mistaken the common approach is to separate memory allocation 
and initialization like this:

	Picture = POINTER TO RECORD
		w, h: INTEGER
	END
		
	Bitmap = POINTER TO RECORD (Picture)
		(*...*)
	END
		
	PROCEDURE InitPicture(p: Picture; w, h: INTEGER);
	BEGIN
		p.w := w;
		p.h := h
	END InitPicture
	
	
	PROCEDURE InitBitmap(b: Bitmap; w, h: INTEGER);
	BEGIN
		InitPicture(b, w, h)
		(*...*)
	END InitBitmap


	PROCEDURE Test;
		VAR bitmap: Bitmap;
	BEGIN
		NEW(bitmap);
		InitBitmap(bitmap, 100, 100)
	END Test


-- August