NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part1/8500

Internet Message Format | 1996-08-05 | 1.9 KB

Path: chronicle.mti.sgi.com!news
From: [e-mail] (Matt Austern)
Newsgroups: comp.lang.c++,comp.lang.c
Subject: Re: Performance: C vs. C++
Date: 15 Feb 1996 23:04:52 GMT
Organization: SGI
Message-ID: <[e-mail]>
References: <[e-mail]> <4da9pn$[e-mail]>
    <[e-mail]>
    <4g0cgt$[e-mail]>
Reply-To: [e-mail]
NNTP-Posting-Host: isolde.mti.sgi.com
In-reply-to: [e-mail]'s message of 15 Feb 1996 22:36:13 GMT

In article <4g0cgt$[e-mail]> [e-mail] (Matt Kennel) writes:

> > And if you do have a pointer to a polymorphic class, and you want to
> > call a virtual function and ensure that you're calling the base
> > class's version, that's actually possible: instead of writing
> > base_pointer->f(), you write base_pointer->base::f().  The syntax
> > is ugly, to be sure, but it doesn't bother me that you have to use
> > ugly syntax for such a rare operation.
>
> Does it work with []??
>
> I.e.
>
>     MyMatrix x;
>
>     x[3][2] = 4;

Yes, but only at the cost of even uglier syntax.  I'm going to pretend
that matrix reference is x(3,2) instead of x[3][2]: you need to jump
through too many hoops if you want to use the x[3][2] form.  (For
those who aren't C++ experts, what you have to do is define an
auxiliary class.)

If x is a reference to a polymorphic base class MatrixBase, and
if operator() is a virtual function, then you can call the base
class version explicitly by writing
    x.MatrixBase::operator()(3,2) = 4.

In general, x(3,2) is equivalent to x.operator()(3,2).  It's only when
you're performing unusual operations, though (like suppressing
run-time dispatch of a virtual function), that you need to write out
x.operator()(3,2) explicitly.
--
Matt Austern
SGI: MTI Compilers Group
[e-mail]