Enum Transition 

pub enum Transition {
    Next(Box<dyn Task>),
    Complete,
}

Transition from one task to the next

When a task executes, it can control the transition to the next state in three different ways. First, it can fail by returning Err. In this case, the runtime will stop execution and handle the error gracefully. Second, a task can succeed and simply trigger the transition to the next task. Third, a task can indicate that the automaton should finish early. This can be useful if no work needs to be done.

Variants

Next(Box<dyn Task>)

Transition to the next task.

Complete

Skip all other tasks and go straight to the teardown task.