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From: jbuck@galileo.berkeley.edu (Joe Buck)
Newsgroups: comp.lang.c++
Subject: Re: distinguishing operator[] on left and right
Message-ID: <11582@pasteur.Berkeley.EDU>
Date: 1 Mar 91 21:07:00 GMT
References: <1991Feb28.212419.20920@ndl.com>
Sender: news@pasteur.Berkeley.EDU
Reply-To: jbuck@galileo.berkeley.edu (Joe Buck)
Lines: 32

In article <1991Feb28.212419.20920@ndl.com>, gilley@ndl.com (Greg Gilley) writes:
|> Is there any way to distinguish when the operator[] is used as an
|> lvalue as opposed to an rvalue?

Yes, something like this:

class ElementRef {
	operator int ();
	operator=(int);
};

class IntVector {
...
	ElementRef operator[] (int);
};

The idea is that [] returns a special class called ElementRef, which
has two operators defined: assignment operator and cast-to-int.
If I say

	IntVector v;
	int i, j;
	...
	v[3] = i;
	j = v[4];

in the first case, ElementRef::operator=(int) is used.  In the
second case, ElementRef::operator int() is used.

--
Joe Buck
jbuck@galileo.berkeley.edu	 {uunet,ucbvax}!galileo.berkeley.edu!jbuck