Re: Mutual dependence

From:
Maxim Yegorushkin <maxim.yegorushkin@gmail.com>
Newsgroups:
comp.lang.c++.moderated
Date:
Mon, 22 Sep 2008 18:33:43 CST
Message-ID:
<f4efa5f6-70b1-465e-ac57-56873d9ae29f@m44g2000hsc.googlegroups.com>
On Sep 20, 7:08 am, lukasz....@gmail.com wrote:

I have two classes representing master and slave. Both come in several
variants:
MasterUnsafe, MasterThreadSafe, ...
SlaveLogging, SlaveIgnore, ...

Now It turns out that they need to call each other's methods. And I
can't afford to have virtualcall
especially when slave is SlaveIgnore and does nothing.
I need to have objects of types of any possible combination like:
MasterUnsafe+SlaveLogging
MasterUnsafe+SlaveIgnore
MasterThreadSafe+SlaveLogging
MasterThreadSafe+SlaveIgnore

I thought that inheritnce can help but I can't get it to work.
I guess I have much to learn :)
Can someone give me some hints?


You could use policy based design, like in http://en.wikipedia.org/wiki/Policy-based_design

Something along these lines:

template<class SafeUnsafe, class LoggingIgnore>
struct master;

template<class SafeUnsafe, class LoggingIgnore>
struct slave
{
    typedef master<SafeUnsafe, LoggingIgnore> master;

    void just_do_it(master* m) { m->do_it_yourself(); }
    void no_you_do_it(master* m) { this->all_right_then(m); }
    void all_right_then(master*);
};

template<class SafeUnsafe, class LoggingIgnore>
struct master
{
    typedef slave<SafeUnsafe, LoggingIgnore> slave;

    slave slave_;

    void do_it() { slave_.just_do_it(this); }
    void do_it_yourself() { slave_.no_you_do_it(this); }
};

int main()
{
    master<int, int> m;
    m.do_it();
}

--
Max

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