Path: news.cs.au.dk!not-for-mail
From: Wilfried Rupflin <wr@irb.cs.uni-dortmund.de>
Newsgroups: comp.lang.beta
Subject: Re: Cannot copy NONE?
Date: 12 Nov 1999 09:22:01 -0000
Organization: University of Dortmund, W-Germany
Lines: 69
Approved: mailtonews@cs.au.dk
Distribution: world
Message-ID: <19991112092201.7475.qmail@noatun.mjolner.dk>
Reply-To: Wilfried Rupflin <wr@irb.cs.uni-dortmund.de>
NNTP-Posting-Host: daimi.cs.au.dk
X-Trace: xinwen.cs.au.dk 942399521 9175616 255.255.255.255 (12 Nov 1999 09:38:41 GMT)
X-Complaints-To: news@cs.au.dk
NNTP-Posting-Date: 12 Nov 1999 09:38:41 GMT
Xref: news.cs.au.dk comp.lang.beta:12163

Hi!

>I found something quite interesting which does not help to generate
>compact code - instead it becomes a bit complicated:
>
>	t,u:^text;
>	do
>	none->t[];
>	t.copy->u[];
>
>	***  THIS GIVES A "REFERENCE ***
>	*** IS NONE" RUNTIME ERROR !! ***

Why not simply ...

	t,u: @text;
	do
	(* ''->t; ... or ... t.clear; ... or ... <nothing> ...
           [in fact: not required here] *)
	t->u;

>Well, normally one would not set a text reference to none, but if I read
>some data into an array (^text) and just want to copy the values (not
>the references!) of the corresponding variables into the array (or to
>any other text reference), it is not possible to do this with small code
>if it's possible that there are NONEs in there.

>Sascha Kimmel

In my experience in most cases where text references are used text
(part) objects would be appropriate. There are a few exceptions only:

Consider e.g.
 
 make_something:
  (#
      t: @text;
      ...
  do ...
  exit t[]
  #)

Since t[] references a part object the whole enclosing object would
be kept which could be pretty big in some cases. (The lesson: don't
use mixed modes, i.e. either

 make_something:
  (#
      t: @text;
      ...
  do ...
  exit t
  #)

or

 make_something:
  (#
      t: ^text;
      ...
  do ... -> t[];
  exit t[]
  #)

 -- unless you know what you are doing, of course.)

Cheers

	Wilfried Rupflin