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Interactions between classes of CEHTL

Figure 1

Basic use (Fig. 1):

You have a certain data "packet" that you want to send to interested listeners. In the diagram, it is the YourEvent class. It is typically a struct with a bunch of const data members and a constructor to initialize them.

Listener< EvType > is an abstract base class template. Your class interested in YourEvent events, called YourListener in Fig. 1, derives from this abstract base class (with the template parameter EvType = YourEvent). Listener< EvType > provides a virtual method, processEvent(const EvType&), to be overriden in YourListener, and provides other concrete methods useful to listeners.

EventSender< EvType > is the dispatcher. It accepts registration by classes that inherit from Listener< EvType >, i.e. objects interested in EvType. It also dispatches EvType events to those listeners when EventSender< EvType>::send(const EvType&) is called.

If one of your listeners for EvType events causes another EvType event to be generated as a consequence of a first EvType being generated, a EventSender< EvType>::IllegalSendError exception will be thrown by the EventSender< EvType>::send() method mentioned above.

More "advanced" uses:

• Time stamping (Fig. 2): the time stamp is not used by any classes of the library, hence it is entirely up to you as to whether or not and how you use such functionality. However, you may elect to do it the following way:
  • TimeStampedEvent< Stamper> is an abstract base class template from which you derive your event type to give it time-stamping;
  • Stamper is a class of your own creation that defines how to create the time stamp; the default time-stamper is DefaultTimeStamper.

Figure 2

• Heterogeneous containers of events (Fig. 3): for storing several different types of events in one container, the class/struct representing EvType can inherit from PolymorphEvent, and be stored in a container, e.g. in std::queue< PolymorphEvent> . PolymorphEvent is an abstract base class that defines a pure virtual send() method for you, which you trivially override to call send< EvType >(). You give each event in the container to EventSender<PolymorphEvent>::send() (or you can call send() directly on the event).

Figure 3

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