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/*!

    \example statemachine/pingpong

    \title Ping Pong States Example

    The Ping Pong States example shows how to use parallel states together

    with custom events and transitions in \l{The State Machine Framework}.

    This example implements a statechart where two states communicate by

    posting events to the state machine. The state chart looks as follows:

    \img pingpong-example.png

    \omit

    \caption This is a caption

    \endomit

    The \c pinger and \c ponger states are parallel states, i.e. they are

    entered simultaneously and will take transitions independently of

    eachother.

    The \c pinger state will post the first \c ping event upon entry; the \c

    ponger state will respond by posting a \c pong event; this will cause the

    \c pinger state to post a new \c ping event; and so on.

    \snippet examples/statemachine/pingpong/main.cpp 0

    Two custom events are defined, \c PingEvent and \c PongEvent.

    \snippet examples/statemachine/pingpong/main.cpp 1

    The \c Pinger class defines a state that posts a \c PingEvent to the state

    machine when the state is entered.

    \snippet examples/statemachine/pingpong/main.cpp 2

    The \c PingTransition class defines a transition that is triggered by

    events of type \c PingEvent, and that posts a \c PongEvent (with a delay

    of 500 milliseconds) to the state machine when the transition is

    triggered.

    \snippet examples/statemachine/pingpong/main.cpp 3

    The \c PongTransition class defines a transition that is triggered by

    events of type \c PongEvent, and that posts a \c PingEvent (with a delay

    of 500 milliseconds) to the state machine when the transition is

    triggered.

    \snippet examples/statemachine/pingpong/main.cpp 4

    The main() function begins by creating a state machine and a parallel

    state group.

    \snippet examples/statemachine/pingpong/main.cpp 5

    Next, the \c pinger and \c ponger states are created, with the parallel

    state group as their parent state. Note that the transitions are \e

    targetless. When such a transition is triggered, the source state won't be

    exited and re-entered; only the transition's onTransition() function will

    be called, and the state machine's configuration will remain the same,

    which is precisely what we want in this case.

    \snippet examples/statemachine/pingpong/main.cpp 6

    Finally, the group is added to the state machine, the machine is started,

    and the application event loop is entered.

  */