Quick inheritance question

[Speedo]

Say that you have a event handler interface like

class KeyboardEventHandler
{
public:
  virtual bool KeyDown(const KeyboardEvent&) = 0;
  virtual bool KeyUp(const KeyboardEvent&) = 0;
};

and implement it something like

class ApplicationState
  : private KeyboardEventHandler
{
private:
  virtual bool KeyDown(const KeyboardEvent&) { return true; }
  virtual bool KeyUp(const KeyboardEvent&) { return true; }
};

With possible later usage looking like

Keyboard kb;
ApplicationState appState;

kb.RegisterEventHandler(&appState);

Is the private inheritance kosher in this case? I want the ApplicationState to behave as-a KB event handler to recieve input, but I don't want the whole world to see the event handler functions - only the Keyboard class that will be sending the events. This compiles and runs fine with MSVC9, I just want to double check that it isn't something being enabled by an MSVC extension.

[Zaccheus@Work]

There's really not enough info here for me to answer the question.

In which function does the following take place?

Keyboard kb;
ApplicationState appState;

kb.RegisterEventHandler(&appState);

No code outside the ApplicationState class should be able to see the private base class.

[Richard.J]

I tend to use private inheritance for such event interfaces as well (influenced by a discussion here which I can't find at the moment), but with g++ I came into situation where a construct like yours led to an error message such as "the interface is not accessible". It work fine, however, if the event class registers itself.

[Speedo]

It work fine, however, if the event class registers itself.

You know, that must've been how I did it before. I was sitting here starting to feel kinda stupid wondering why the example code didn't work after all...