Path: news.daimi.aau.dk!glad
From: Rene Wenzel Schmidt <rws@daimi.aau.dk>
Newsgroups: comp.lang.beta
Subject: Re: UNION in BETA
Date: 20 Mar 1996 10:07:24 GMT
Organization: DAIMI, Computer Science Dept. at Aarhus University
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> From news@gjallar.daimi.aau.dk Wed Mar 20 08:45:45 1996
> To: usergroup@mjolner.dk
> From: Kolbjorn.Aambo@ub.uio.no (Kolbj\xrn Aamb\x)
> Subject: UNION in BETA
> Date: Tue, 19 Mar 1996 12:08:15 +0100
> Nntp-Posting-Host: ubmac86.uio.no
> X-Charset: LATIN1
> X-Char-Esc: 29
> 
> In C I can define
> 
> struct cell {
>    union {
>       long int;
>       short int n[2];
>       unsigned char c[4];
>    };
> };
> 
> 
> 
> cell s;
> 
> 
> Here c can be regarded as a integer
> 
> s = 234;
> 
> s.n[0] = 'ab'; said another way:
> 
> s.c[0] = 'a';
> s.c[1] = 'b';
> 
> 
> Can something like this be expressed in BETA now or in the future?
> 

If you want to be able to access an integer as an array of char, or
do similar type-unsafe things the answer is no (present, and highly
likely in the future).

On the other hand, if you are using a union to save memory, it can
easily be done using polymorphism. For example:

Cell: (##);
IntCell: Cell(# i: @integer #);
CharCell: Cell(# c: [4]@Char #);
....

Then you can choose the optimal representation of a Cell at runtime, not 
having to allocate memory for an integer if it contains an array of char and
vice-versa. To access the cell you need to check its type first. 

/Rene