NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part1/6448

Text File | 1996-08-05 | 1.7 KB | 48 lines

Path: dawn.mmm.com!news
From: [e-mail] (Kevin J Hopps)
Newsgroups: comp.lang.c++
Subject: Re: Virtual Function in private part?
Date: 8 Feb 1996 14:17:52 GMT
Organization: 3M - St. Paul, MN  55144-1000 US
Message-ID: <4fd0mg$[e-mail]>
References: <4f7s5g$[e-mail]>
Reply-To: [e-mail]
X-Newsreader: TIN [version 1.2 PL2]

Hong Shen ([e-mail]) wrote:
> Is there any reasons to make a member function in the private section of
> a class virtual?

The decisions about whether to make a function private or virtual are
orthogonal.  You make a function private if you want no derived classes
to call it.  You make a function virtual if you want to allow derived
classes to override it.

This may seem like a contradiction, but consider this example:

class Mutex
{
public:
    ...
    void lock() { doSomeStuff(); do_lock(); doSomeOtherStuff(); }
    ...
private:
    void doSomeStuff();
    void doSomeOtherStuff();
    virtual void do_lock() = 0;
};

In this example, the intent is that a derived class must provide the
do_lock() function, but that the only way to call it is through the
lock() function.  Of course there is no way to prevent the derived
class from calling do_lock() directly, but at least further derivatives
will be unable to call it.
--
Kevin J. Hopps                  e-mail: [e-mail]
3M Company                      phone:  [phone]
3M Center, Bldg. 235-2D-57      fax:    [phone]
St. Paul, MN 55144-1000         Opinions are my own.  I don't speak for 3M.
    But 3M speaks for me -- I did not write the following line:

Opinions expressed herein are my own and may not represent those of 3M.