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From: len@geac.UUCP (Leonard Vanek)
Newsgroups: comp.lang.c++
Subject: Re: Structures want anonymity, too.
Message-ID: <583@geac.UUCP>
Date: Mon, 16-Mar-87 13:38:07 EST
Article-I.D.: geac.583
Posted: Mon Mar 16 13:38:07 1987
Date-Received: Tue, 17-Mar-87 01:20:57 EST
References: <165700008@uiucdcsb> <1062@valid.UUCP>
Reply-To: len@geac.UUCP (Leonard Vanek)
Organization: Geac Computers Intl. Toronto, CANADA
Lines: 45
Summary: Why not provide variant records directly instead?

In article <1062@valid.UUCP> roger@valid.UUCP (Roger H. Scott) writes:
>We (Valid Logic Systems, Inc.) have modified our 1.1 C++ translator to
>allow anonymous structures as well as anonymous unions.  Our primary motivation
>for this enhancement was for use with our Pascal-to-C++ translator that we
>are developing.  In Pascal there is a construct known as a "variant record"
>that takes the following form (from Jensen & Wirth, 2nd Edition, pp. 42 & 45):
>
He then goes on to explain the need for the following syntax for
emulating a pascal variant record:
>
>typedef struct {
>	int a;
>	union {
>		struct {
>			int b, c, d; float e;
>		};
>		struct {
>			char f[11]; random_type_name g;
>		};
>	};
>} variant_record_example;

This is certainly the minimal change to achieve the desired
result and may be preferred for precisely that reason. However,
it strikes me that if what is wanted is a way to get variant
records in C++ (not just for Pascal to C translators but also for
original code) why not look for a way to eliminate all of the
redundant syntax to come up with a clean ``variant structure''
mechanism? Perhaps it could be modelled on the switch statement
in much the same way that Pascal and Ada model their variant
records on their case statements?

I have not thought this idea out so it may not be all that good,
but as long as Bjarne and other readers of this newsgroup are
considering the small change maybe you should consider the larger
one as well.

---------------------------------------------------------------------
Leonard Vanek                       phone (416) 475-0525
Geac Computers International
350 Steelcase Rd. West
Markham Ontario L3R 1B3
Canada

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