🚀 go-pugleaf

In article <1992Nov11.134940.19557@titan.tsd.arlut.utexas.edu> larry@tsd.arlut.utexas.edu (Larry Maturo) writes:
>In article <1992Nov11.102409.12183@jyu.fi> sakkinen@jyu.fi (Markku Sakkinen) writes:
>> ...
>>That has obviously been the main reason for eliminating enumerations.
>>And even this rationale is very weak.  Only record types can be extended
>>in Oberon, not atomic types nor arrays.
>>
>Enumerations are often used as the discriminent in variant records.  In Oberon
>you declare different records that are extensions of a common record.  You also
>delcare a different pointer type to each one and the type name of the pointer
>takes the place of the enumeration so you get the effect of enumerations, but
>it's extendable over module boundries.  Pretty neat!

That's only one of the many useful purposes of enumerations!
Furthermore, Oberon's type extensions cannot do all the things
that are possible with tagged variant records (and vice versa).
With variant records, you can change the variant of the object itself.
With type extensions, you can only make a pointer point at an object
of another related type:  that does not affect the original object
nor any other pointers to it.

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Markku Sakkinen (sakkinen@jytko.jyu.fi)
       SAKKINEN@FINJYU.bitnet (alternative network address)
Department of Computer Science and Information Systems
University of Jyvaskyla (a's with umlauts)
PL 35
SF-40351 Jyvaskyla (umlauts again)
Finland
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