Useful Design Patterns for Game Development - Learn C++ for Game Development - page 230

The Notify template method specifies a method pointer parameter. The method pointer must have a
void return type and take no arguments. The type of a method pointer takes the following format.
void (Class::*VariableName)()
Class here represents the name of the class the method belongs to and VariableName is the name
we use to reference the method pointer in our code. You can see this in action in the Notify method
when we call the method using the Method identifier. The object we are calling the method on here is
an Observer* and the address of the method is dereferenced using the pointer operator.
Once our Notifier class is complete, we can use it to create Notifier objects. Listing 23-9 inherits
a Notifier into the QuitOption class.
Listing 23-9. Updating QuitOption
class QuitOption
: public Option
, public Notifier<QuitObserver>
{
public:
QuitOption(const std::string& outputText)
: Option(PlayerOptions::Quit, outputText)
{
}
virtual void Evaluate(Player& player);
};
QuitOption now inherits from the Notifier class, which is passed a new class as its template
parameter. Listing 23-10 shows the QuitObserver class.
Listing 23-10. The QuitObserver Class
class QuitObserver
{
public:
virtual void OnQuit() = 0;
};
QuitObserver is simply an interface that provides a method, OnQuit , to deriving classes. Listing 23-11
shows how you should update the QuitOption::Evaluate method to take advantage of the Notifier
functionality.
Listing 23-11. Updating QuitOption::Notifier
void QuitOption::Evaluate(Player& player)
{
Notify<&QuitObserver::OnQuit>();
}