NetNews Usenet Archive 1992 #20/NN_1992_20.iso/spool/comp/std/cplus/1147

Text File | 1992-09-10 | 1.5 KB | 44 lines

Newsgroups: comp.std.c++
Path: sparky!uunet!brunix!brunix!sdm
From: [e-mail] (Scott Meyers)
Subject: Re: Zero-length structures and pointer comparisons
Message-ID: <[e-mail]>
Sender: [e-mail]
Organization: Brown University Department of Computer Science
References: <[e-mail]> <[e-mail]> <[e-mail]>
Date: Thu, 10 Sep 1992 15:32:02 GMT
Lines: 32

In article <[e-mail]> [e-mail] (Markku Sakkinen) writes:
| In article <[e-mail]> [e-mail] (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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