Question

I have a pretty simple game engine. It uses several singletons(I’ll enumerate some of them).

Resource Manager
Render Engine
Events Manager
Factory
etc

These singletons have many calls from one to another. I’ll take Events Manager sample usage:

1. Any object derived from Listener can add itsel as a listener for some events just like this EventsManager->RegisterListener(this, &SomeClass::SomeMethod); (event type is deduced by SomeMethod parameter)
2. Any other object can fire an event like this EventsManager->PushEvent(SomeEvent);

After some synchronization the event reaches to all listeners. This is very a simple usage for EventsManager when it is singleton.

Similar behavior is with other singletons. I want to remove the singletons, but my main problem is that I want to keep the code simple to use from the “user point of view” as it is now. I read some techniques of doing this, but most of the make the initialization/usage of the classes more complicated. I know this topic was discused many times on SO, but no answer is appropriate for my programming philosophy – to keep everything as simple as possible.

I don’t want to have complicated definition/initialization for my classes like:

SomeClass<EventManager, RenderEngine,...>

or

SomeClass::SomeClass(EventsManager, RenderEngine...)

Can you please give me some advice on this topic?

Answer 1

You could have a global “game” object that creates an instance of each of the classes that are currently singletons

For the specific example of your EventManager; your Listener base class could provide implementations of a register method and a push method that derived classes can call.

A skeleton definition:

class Listener
{
public:
    virtual void ReceiveMessage( ... ) = 0;

protected:
    void Register()
    {
        GetEventManagerSomehow()->RegisterListener( this, etc );
    }

    void PushEvent( etc )
    {
        GetEventManagerSomehow()->PushEvent( etc );
    }

}