def init ( method )
      raise TypeError, error_message(method, __method__) unless method.instance_of? Method
      @init = method
    end
def init ( method )
      raise TypeError, error_message(method, __method__) unless method.instance_of? Method
      @init = method
    end
call-seq:
  State.new( String )
 call-seq:
   init( method(:some_init_method) )

 Set initializer method for current state.