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From: wmmiller@cup.portal.com (William Michael Miller)
Newsgroups: comp.lang.c++
Subject: Re: operator delete -- static AND virtual ????
Message-ID: <30161@cup.portal.com>
Date: 24 May 90 00:48:06 GMT
References: <401@mole-end.UUCP> <29839@cup.portal.com> <413@mole-end.UUCP>
Organization: The Portal System (TM)
Lines: 47

mat@mole-end.UUCP (Mark A Terrbile) writes:
> when I write
>
>         delete xp;
>
> I am invoking a delete operator.

Aha, here's part of the problem.  There is a difference between the delete
operator and operator delete().  The definition of the delete operator is
that it invokes the destructor, if any, and then invokes operator delete().
This unfortunate overlapping of terminology is bound to be confusing, but
it's too late now to fix it.  (I've been told that originally destructors
were member functions named "delete()" instead of ~classname(); that would
have been preferable from several perspectives.  Not only would it have
avoided this particular confusion, but it would have made virtual
destructors work like other virtual functions -- virtual destructors are the
only virtual functions for which the name of the overriding function is
*different* from the name of the base class function!)

> The effect is that the delete operator that is invoked depends upon the actual
> type of the complete object, and that is the behavior which I usually expect
> of a virtual function.

You're absolutely right on this point; I didn't catch it from your original
posting.  The fact that you may end up invoking a derived class operator
delete() even though you used a base class pointer for the delete operator
is *not* spelled out in the manual, and a clear statement of this fact (or
the contrary, although I think most would agree with you about the
desirability of this behavior) is definitely needed.  Thanks for pointing
that out.

> The exact words of the reference manual are that operator delete is static.

In some sense, calling operator delete() "static" is arbitrary and a bit
misleading; the only thing operator delete() has in common with static
member functions is the absence of a "this" pointer.  The main idea of
static member functions is that they can be invoked by the
classname::member() syntax, i.e., without referring to a particular object,
but that makes no sense for operator delete(): it has to be accessed via an
object, although the object will have been destroyed before operator
delete() gets control.  I think X3J16 may want to visit this issue of
terminology as well.

Sorry for missing part of your meaning the first time 'round.

-- William M. (Mike) Miller, Glockenspiel, Ltd.
   wmmiller@cup.portal.com