Re: Is finalizing a virtual method possible in C++?

From:

Jeff Schwab <jeff@schwabcenter.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 22 Feb 2008 11:43:37 -0800

Message-ID:

<yfOdnWokQrdeuCLanZ2dnUVZ_qCunZ2d@comcast.com>

Alf P. Steinbach wrote:

* Kira Yamato:

On 2008-02-22 07:35:34 -0500, Pavel Lepin <p.lepin@ctncorp.com> said:

Kira Yamato <kirakun@earthlink.net> wrote in
<2008022206570016807-kirakun@earthlinknet>:

So, I don't want to say too hestantly that it is
impossible to simulate the finalizing of virtual methods
and classes in C++.

Hence, I rather turn to the experts and ask if anyone
knows if it is possible to simulate them in any way?

This is a FAQ.

<http://www.parashift.com/c++-faq-lite/>

Yes. Thanks. But the FAQ does not say that finalizing method is
impossible. If in fact it did, then the answer is found. Instead, it
just proposes a "solution."

So let me try asking differently, has anyone gotten further with a
better solution than merely stating a comment?

There should be no reason to finalize a member function in C++.

But if you absolutely must it's not that difficult.

    class Base
    {
    friend class Derived;
    private:
        struct OverrideTag {};
    public:
        virtual void foo( OverrideTag = OverrideTag() ) = 0;
    };

    class Derived: public Base
    {
    public:
        virtual void foo( OverrideTag = OverrideTag() ) {}
    };

    class FurtherDerived: public Derived
    {
    public:
        // Nix njet.
    // virtual void foo( OverrideTag = OverrideTag() ) {}
    };

    int main()
    {
        Derived o;
        o.foo();
    }

What's to stop somebody from making OverrideTag public in the derived
class? [1]

struct Derived: Base {
using Base::OverrideTag;
virtual void foo( OverrideTag = OverrideTag() ) { }
};

[1] I was confused by something like this a couple months ago, and
posted a question about it (here, I think). I got a few explanatory
responses of the form "What do you mean you didn't think of that?
Everybody knows that, and you have no right to find it confusing." I
love the fact that people find everything obvious, just as soon as it
has been pointed out to them. :)