Re: Should component know its host?

From:

"Daniel T." <daniel_t@earthlink.net>

Newsgroups:

comp.lang.c++

Date:

Thu, 14 Aug 2008 20:29:43 -0400

Message-ID:

<daniel_t-BE9363.20294314082008@earthlink.vsrv-sjc.supernews.net>

Krice <paulkp@mbnet.fi> wrote:

There is a component class inside the host class:

class Host
{
Component *c;
...

In some cases Component needs to call the host and
I guess the only way is that you pass the host for it:

Component::Component(Host *h)
{
h->Do_Something();
...

Somehow I think this is bad design, but how to avoid it?

The typical OO solution is to make an abstract base class:

class HostBase {
public:
   virtual void Do_Something() = 0;
};

class Base : public HostBase {
public:
   void Do_Something();
};

class Component {
public:
   Component( HostBase* hb ) {
      hb->Do_Something();
   }
};

I'm not so sure, though, if this is the best solution in this case... If
the component really is "inside" the host, then maybe the host should
call Do_Something() itself before constructing the component. If the
component is being created outside the host and passed into it, then
maybe the creator of the component should be calling Do_Something() on
the host.