Ruby, RGSS & General Code Discussion

[Kain Nobel]

I found an interesting little tidbit today! Actually I've found it before and forgot about it, but since I've been reminded...

Game_Battler#add_state

Notice
how in the definition of add_state, the definition calls itself?
This is from the default script, but I'm curious why it doesn't throw a
Stack Level Too Deep or something.

Code:

#--------------------------------------------------------------------------
  # * Add State
  #     state_id : state ID
  #     force    : forcefully added flag (used to deal with auto state)
  #--------------------------------------------------------------------------
  def add_state(state_id, force = false)
    # For an ineffective state
    if $data_states[state_id] == nil
      # End Method
      return
    end
    # If not forcefully added
    unless force
      # A state loop already in existance
      for i in @states
        # If a new state is included in the state change (-) of an existing
        # state, and that state is not included in the state change (-) of
        # a new state (example: an attempt to add poison during dead)
        if $data_states[i].minus_state_set.include?(state_id) and
           not $data_states[state_id].minus_state_set.include?(i)
          # End Method
          return
        end
      end
    end
    # If this state is not added
    unless state?(state_id)
      # Add state ID to @states array
      @states.push(state_id)
      # If option [regarded as HP 0]is effective
      if $data_states[state_id].zero_hp
        # Change HP to 0
        @hp = 0
      end
      # All state loops
      for i in 1...$data_states.size
        # Dealing with a state change (+)
        if $data_states[state_id].plus_state_set.include?(i)
          add_state(i)
        end
        # Dealing with a state change (-)
        if $data_states[state_id].minus_state_set.include?(i)
          remove_state(i)
        end
      end
      # line change to a large rating order (if value is the same, then a
      # strong restriction order)
      @states.sort! do |a, b|
        state_a = $data_states[a]
        state_b = $data_states[b]
        if state_a.rating > state_b.rating
          -1
        elsif state_a.rating < state_b.rating
          +1
        elsif state_a.restriction > state_b.restriction
          -1
        elsif state_a.restriction < state_b.restriction
          +1
        else
          a <=> b
        end
      end
    end
    # If added forcefully
    if force
      # Set the natural removal's lowest number of turns to -1
      @states_turn[state_id] = -1
    end
    # If not added forcefully
    unless  @states_turn[state_id] == -1
      # Set the natural removal's lowest number of turns
      @states_turn[state_id] = $data_states[state_id].hold_turn
    end
    # If unable to move
    unless movable?
      # Clear action
      @current_action.clear
    end
    # Check the maximum value of HP and SP
    @hp = [@hp, self.maxhp].min
    @sp = [@sp, self.maxsp].min
  end

There
is a way for a method to call itself within its own definition,
but that is via the use of alias or alias_method. A child
method can call the definition of a parent's method by using a
super, a parent method can call other methods defined by it's
child class even if its not defined within its own class, but a method calling itself
just seems odd to me.

A freshly defined method shouldn't be able to call itself within it's own definition, should it?