Path: news.daimi.aau.dk!sbrandt
From: sbrandt@daimi.aau.dk (S|ren Brandt)
Newsgroups: comp.lang.beta
Subject: Re: How to obtain a ref. to current _component_ obj.?
Date: 1 May 1995 13:16:05 GMT
Organization: DAIMI, Computer Science Dept. at Aarhus University
Lines: 80
Message-ID: <3o2mul$2vn@belfort.daimi.aau.dk>
References: <3nj0if$6hh@fbi-news.informatik.uni-dortmund.de>
NNTP-Posting-Host: quercus.daimi.aau.dk
Keywords: component,current,this

Thus spake warda@fbi-news (Armin M. Warda):

>Why is the following illegal for the BETA-Compiler [Mjolner BETA System 
>version 5.0(2) for SUN-4]?

>    (# Process: 
>         (# me: ^|Process;
>         do this(Process)[]->me[];
>            INNER
>        #);
>       A: @|Process (# do 'A' -> putline #);
>    do A;
>    #)


Because assignment between component and object references has
not been implemented by the current compiler. It is easily handled, 
but has not been done.

>This error message is displayed by the compiler:

>    THIS(Process)[]->me[]
>    ***** Illegal assignment/comparison of value, reference or repetition

The following code provides a work-around for assigning component references
to object references and vice versa.
Please ignore that objectToComponent exploits undocumented low-level features 
of the compiler.

   INCLUDE '~beta/sysutils/v1.4/objinterface';
   ---lib:attributes---
   objectToComponent:
     (# o: ^Object;
	c: ^|Object;
	ato: @addressToObject;
     enter o[]
     do (if o[]<>NONE then
	    (if (o[]->getGCField)//-6 then
		(if ((@@o->tos'%AdrGetLong')-24->tos'%AdrGetLong')
		 //ComponentPTvalue then
		    (@@c,(@@o->tos'%AdrGetLong')-24)->assignRef
		if);
	    if);
	if);
     exit c[]
     #);

   example:
     (# o: ^Process;
        c: ^|Process;
     do ...;
        o[]->objectToComponent->c[];
        ...;
        c[]->componentToObject->o[];
     #);

>Is there a construct to obtain a reference to the current _component_ object?
>=============================================================================
#)

I'm not sure whether you want this to solve the problem above, or whether
you need it for other purposes... If you are using systemenv, you can
always get a reference to the currently executing component by reading
the systemenv attribute "theActive". See "basicsystemenv.bet".

If you are not using systemenv, there is currently no interface to get a 
reference to the current component object (although the information is
of course available in the runtime system.)

  -- Soren

>Is there a work-around for this problem?
>========================================
>Yours sincerely, Armin.
>---------------------------------------------------------------------
>Armin M. Warda                 <warda@ls4.informatik.uni-dortmund.de>
>Universitaet Dortmund, Informatik IV, GB V, R.503, Tel: 0231-755-4824
>44221 Dortmund,  Privat: <warda@nephilim.ruhr.de>, Tel: 0231-75-37-30
>WWW:  "http://ls4-www.informatik.uni-dortmund.de/QM/MA/warda/pi.html"
>PGP fingerprint  =   66 C0 3E 8E D9 FE 61 77  DB 37 0D 40 36 53 71 6A