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From: sdm@cs.brown.edu (Scott Meyers)
Subject: Re: Zero-length structures and pointer comparisons
Message-ID: <1992Sep10.153202.23881@cs.brown.edu>
Sender: news@cs.brown.edu
Organization: Brown University Department of Computer Science
References: <9225302.22791@mulga.cs.mu.OZ.AU> <4945@holden.lulea.trab.se> <1992Sep10.094957.23588@jyu.fi>
Date: Thu, 10 Sep 1992 15:32:02 GMT
Lines: 32

In article <1992Sep10.094957.23588@jyu.fi> sakkinen@jyu.fi (Markku Sakkinen) writes:
| In article <4945@holden.lulea.trab.se> jbn@lulea.trab.se (Johan Bengtsson) writes:
| >
| >const T& operator = ( const T& t )
| >{
| >	if ( &t == this ) return;	// avoid self-assignment
| >	// ...
| >}
| >
| >Is the above idiom broken?
| 
| Oh dear, why have I not noted this _horrible_ defect in the language
| definition before?  Probably because it was too bad to be suspected.
| The above idiom is certainly common, and it is used in Stroustrup's
| own books.  The first example I could found now in "The C++ P. L." (2. ed.)
| is in 8.3.3 (p. 266).

The idiom is clearly older than that.  Stroustrup uses it in the FIRST
edition of his book, section 6.6, p. 179:

    void String::operator=(String& a)
    {
        if (this == &a) return;  // beware of s=s;
        ...

It would certainly cause grief to many a program if this were to suddenly
be found to be unportable.

Scott

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