Should component know its host?

[Krice]

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?

 

[mlimber]

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?

You could use a generic callback mechanism. Check out
std::tr1::function if you have TR1 available or Boost.Function if you
don't. It would make your code look something like:

Component::Component( const std::tr1::function& prologFn )
{
prologFn();
// ...
}

Also similar is _Modern C++ Design_'s Loki::Function (http://loki-
lib.sourceforge.net).

Cheers! --M

 

[Krice]

You could extract the behaviour the component needs into a separate
class and derive your host from that class.

I want to avoid deriving.. anyway, the solution was simple
after all. I wanted to control the host from the component,
but I guess it should be the other way around so now the host
is controlling the (now simplified) component.