Re: virtual functions and access specifiers

From:

"Bo Persson" <bop@gmb.dk>

Newsgroups:

comp.lang.c++.moderated

Date:

Tue, 4 Nov 2008 16:45:03 CST

Message-ID:

<6nbondFk83dqU1@mid.individual.net>

Hicham Mouline wrote:

Hello,
I have looked at
(1) http://www.parashift.com/c++-faq-lite/strange-inheritance.html
and then at
(2) http://www.gotw.ca/publications/mill18.htm
They seem to give opposite advise.

In particular, (2) gives these guidelines:
Guideline #1: Prefer to make interfaces nonvirtual, using Template
Method. Guideline #2: Prefer to make virtual functions private
Guideline #3: Only if derived classes need to invoke
the base implementation of a virtual function, make the virtual
function protected.

while (1) says:
[23.3] Should I use protected virtuals instead of public virtuals?
The cheapest + fastest + lowest risk approach in my experience ends
up resulting in most virtuals being public

[23.4] When should someone use private virtuals?
Almost never.

(1) seems to say that virtuals should be (end up being) public,
while (2) says they should be private unless there is a reason to
make them public.

for (1) is it just because when a virtual function is private, then
dervived

class developers

might think they cannot override it?

If i am starting a new project, if I think people will not be
confused by the private virtuals,

should I stick to (2) ?

These are the opinions of different people. :-)

It is true that developers coming from other languages, likeJava, just
know that (2) is impossible, because that's the way it is in their
other language. You have to decide if that is a good reason to make
C++ code look more like Java.

Bo Persson

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