Re: Public virtual harmful? (was Re: Testing Program Question)

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 3 Mar 2010 10:21:47 -0800 (PST)

Message-ID:

<04866490-47e0-4504-a955-1b17c3b99452@g26g2000yqn.googlegroups.com>

On 3 Mar, 04:32, Brian <c...@mailvault.com> wrote:

On Mar 2, 5:20 pm, James Kanze <james.ka...@gmail.com> wrote:

On Feb 28, 4:38 pm, Jorgen Grahn <grahn+n...@snipabacken.se> wrote:

On Wed, 2010-02-17, James Kanze wrote:

On Feb 16, 11:49 am, "Leigh Johnston" <le...@i42.co.uk> wrote:

[...]

These are only "exceptions" to some stupid rule that
only a subset of the C++ community happen to agree with
including yourself.

The "subset" includes most of the experts. People like Herb
Sutter, for example.

I don't want to get involved in an old argument, but James,
where can I read more about the reasoning behind this? It was
a new opinion to me; I don't think I've come across it before.

The article which brought the idea into mainstream programming
ishttp://www.gotw.ca/publications/mill18.htm, by Herb Sutter.

That article says, "Don't derive from concrete classes."

Citing another document which explains why.

I don't know of a better way to support multiple versions
of a client. The versioning that some well-known
serialization libraries tout encourages people to use one
class and conditionals to support multiple versions within
the class. I think that approach is very weak and that
deriving from a concrete class is the better alternative.

I'm not sure. I've never seen an implementation of verionning
which used derivation. I'm not sure it can be made to work, but
perhaps I'm just misunderstanding what you're proposing.

--
James Kanze