state_machine

StateMachine::Machine#after_failure

Creates a callback that will be invoked *after* a transition failures to
be performed so long as the given requirements match the transition.

See +before_transition+ for a description of the possible configurations
for defining callbacks.  *Note* however that you cannot define the state
requirements in these callbacks.  You may only define event requirements.

= The callback

Failure callbacks get invoked whenever an event fails to execute.  This
can happen when no transition is available, a +before+ callback halts
execution, or the action associated with this machine fails to succeed.
In any of these cases, any failure callback that matches the attempted
transition will be run.

For example,

  class Vehicle
    state_machine do
      after_failure do |vehicle, transition|
        logger.error "vehicle #{vehicle} failed to transition on #{transition.event}"
      end
      
      after_failure :on => :ignite, :do => :log_ignition_failure
      
      ...
    end
  end

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