Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!apple!netcom!sjsumcs!horstman
From: horstman@mathcs.sjsu.edu (Cay Horstmann)
Newsgroups: comp.lang.c++
Subject: Re: Distinguishing lvalue/rvalue operator[]
Message-ID: <1991Mar7.003202.16879@mathcs.sjsu.edu>
Date: 7 Mar 91 00:32:02 GMT
References: <1991Mar3.202134.17812@mathcs.sjsu.edu> <1991Mar4.054915.19566@mathcs.sjsu.edu> <1991Mar5.021423.22117@world.std.com>
Organization: San Jose State University - Math/CS Dept.
Lines: 29

In article <1991Mar5.021423.22117@world.std.com> wmm@world.std.com (William M Miller) writes:
>horstman@mathcs.sjsu.edu (Cay Horstmann) writes:
>> I was thinking more about Joe Buck's suggestion to make the distinction
>> of lvalue/rvalue operator[] by returning an access class, and found another
>> snag. Suppose you have a variable size integer array and have operator[]
>> return an instance of class Access with functions
>>      Access::operator=(int)
>>      Access::operator int
>> as suggested. Then the statement
>>      a[i]++
>> will not execute.
>
>Of course not.  (You wouldn't want it to, anyway -- presumably whatever you
>do in operator=() to handle lvalue access also needs to be done for ++, no?)
>The "Access" class is really acting as an enhanced functionality surrogate
>for the addressed member (enhanced functionality because it's supposedly
>doing different things for lvalue and rvalue accesses).  That means that
>anything you want to do with the accessed array member, you must be able to
>do with an object of class Access.  If you want to use ++, you need an
>Access::operator++().  If you want to do ".print()," as in your earlier
>posting, you need an Access::print().  It's really very straightforward --
>you look at what you need to do with selected array elements and you put the
>appropriate support in the corresponding Access class.
>
Not as straightforward as you say. I am writing a template. I have no way
of knowing what methods X includes, so I cannot manually replicate them
in the access class. 

Cay