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From: lsr@Apple.com (Larry Rosenstein)
Newsgroups: comp.sys.mac.programmer
Subject: Re: C++ CString sample code
Message-ID: <11830@goofy.Apple.COM>
Date: 24 Jan 91 01:56:18 GMT
References: <5672@rex.cs.tulane.edu>
Sender: usenet@Apple.COM
Organization: Apple Computer, Inc.
Lines: 26

In article <5672@rex.cs.tulane.edu>, mandel@vax.anes.tulane.edu (Jeff E Mandel MD MS) writes:
> 
> From: Reid Ellis <aliasbridge!Reid_Ellis.STYLE%alias@VM.TCS.Tulane.EDU>
> 
> >Why is it
> >    void operator +=( const CString& s1);
> >and not
> >    CString& operator +=( const CString& s1);
> >??
> >
> >                                                  Reid
> 
> The answer is subtle. An operator has access to the object which invokes
> it. The operator simply modifies the existing object, rather than
> returning a new one. Thus:

You could write operator+= either way, depending on what behavior you wanted
to provide.  For example, for built-in types, you can write something like 

			x = (y += z),

which  adds z to y and assigns the result to x.  

If CString::operator+= returns void, then this kinds of statement is illegal.

To allow it, you would have operator+= return a const CString&.