state_machine

StateMachine::Callback.bind_to_object=

Determines whether to automatically bind the callback to the object
being transitioned.  This only applies to callbacks that are defined as
lambda blocks (or Procs).  Some integrations, such as DataMapper, handle
callbacks by executing them bound to the object involved, while other
integrations, such as ActiveRecord, pass the object as an argument to
the callback.  This can be configured on an application-wide basis by
setting this configuration to +true+ or +false+.  The default value
is +false+.

*Note* that the DataMapper and Sequel integrations automatically
configure this value on a per-callback basis, so it does not have to
be enabled application-wide.

== Examples

When not bound to the object:

  class Vehicle
    state_machine do
      before_transition do |vehicle|
        vehicle.set_alarm
      end
    end
    
    def set_alarm
      ...
    end
  end

When bound to the object:

  StateMachine::Callback.bind_to_object = true
  
  class Vehicle
    state_machine do
      before_transition do
        self.set_alarm
      end
    end
    
    def set_alarm
      ...
    end
  end

Source | Google | Stack overflow