Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!pasteur!helios.ee.lbl.gov!nosc!cod!mball
From: mball@cod.NOSC.MIL (Michael S. Ball)
Newsgroups: comp.lang.c++
Subject: Re: Overloading operator new()
Message-ID: <1239@cod.NOSC.MIL>
Date: 5 Oct 88 01:56:18 GMT
References: <5949@june.cs.washington.edu>
Reply-To: mball@cod.nosc.mil.UUCP (Michael S. Ball)
Organization: Naval Ocean Systems Center, San Diego
Lines: 37

In article <5949@june.cs.washington.edu> david@uw-june.UUCP (David Callahan) writes:
>Stroustrup lists the "new" operator as one that can be
>overloaded. I'm not exactly sure what functionality this
>provides (over assigning into "this" in the constructor)
>and I know I can't get the syntax right. Could someone
>show me an example of "new" being overloaded and how
>it would be used?

As far as I know, the feature is documented only in the "Evolution of C++"
paper in the Santa Fe workshop proceedings.  The syntax is simple:

class foo {
    :
    :
  void * operator new(long);
    :
};

Your version of cfront may not accept it, however, as it is a recent addition
to the language.

It adds no new functionality over assignment to this, but is less error-prone
and puts all of the allocation code in one place, rather than replicated
in each constructor.  Assignment to "this" has a number of traps into which
one may fall.  For example, you must make sure that there is an assignment
to this on all possible paths through the constructor.  Otherwise, member
constructors may not be called.  Overloading "operator new" seems much cleaner.

A side effect is that the resulting code will probably be better since the
member and base class initializations do not have to be replicated as they
do when "this" is assigned to.

Mike Ball
TauMetric Corporation
1094 Cudahy Pl. Ste 302
San Diego, CA 92110
(619)275-6381