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From: kraus@uiucdcsb.UUCP
Newsgroups: comp.lang.c++
Subject: Structures want anonymity, too.
Message-ID: <165700008@uiucdcsb>
Date: Sat, 28-Feb-87 16:51:00 EST
Article-I.D.: uiucdcsb.165700008
Posted: Sat Feb 28 16:51:00 1987
Date-Received: Mon, 2-Mar-87 03:49:47 EST
Lines: 45
Nf-ID: #N:uiucdcsb:165700008:000:1416
Nf-From: uiucdcsb.cs.uiuc.edu!kraus    Feb 28 15:51:00 1987


Anonymous unions are nice.  For example, page 67 of the C++ book
gives the following example:

    struct entry {
        char* name;
        char type;
        union {
            char* string_value;     // used if type=='s'
            int int_value;          // used if type=='i'
        };
    };

If "x" is an "entry", then one can get to the fields in the union
with "x.string_value" and "x.int_value".  (In C, one would have to
give the union a name, which is annoying.)

But why aren't there anonymous structures, too?  For example, suppose
that for some reason I also needed a flag in case type=='i'.  I would
like to say

        union {
            char* string_value;
            struct { int int_value; int flag; };
        };

But this does not seem to be allowed.  (I believe that it was version 1.1
that I tried this on.)  So, I am forced to put "int flag" at the top level
of the structure, which is annoying.  It gets worse when lots of cases
need several fields.  The clearest solution that I have found is to have
several anonymous unions in succession.

It also seems the me that adding anonymous structures would increase the
orthogonality of the language.


Tim Kraus
Department of Computer Science
University of Illinois at Urbana-Champaign
1304 West Stringfield Avenue
Urbana, IL  61801

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