Ruby class inheritance

Question

I defined a node class and player class as following:

class Node < OpenStruct
  def initialize(parent,tag,&block)
    super()
    self.parent = parent
    self.parent.children << self unless parent.nil?
    self.children = []
    self.tag = tag
    instance_eval(&block) unless block.nil?
  end
end

class Player < Node
  def initialize(parent)
    Node.new(parent,:player) do 
      self.turn_num = 1
    end
  end
end

The instance variable player was created by

player = Player.new(room) # room is the parent node which was defined
puts player.turn_num

And I got the error:

in `method_missing': undefined method `[]' for nil:NilClass (NoMethodError)

Could you help me figure out where went wrong? Thanks!

Edit:

The problem should be the initialize in the Player class. I changed my codes

class Player < Node
      def self.new(parent)
        Node.new(parent,:player) do 
          self.turn_num = 1
        end
      end
 end

Then there is no error.What's wrong with the initialize here?

The error message is pretty self explanatory: you have a nil and you are trying to do stuff with it. — tckmn
– tckmn, Commented Nov 18, 2012 at 5:15
@PicklishDoorknob Sure. I wanted to figure out where generated a nil. I found player is not a nil — Yujun Wu
– Yujun Wu, Commented Nov 18, 2012 at 5:19
@PicklishDoorknob .rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/ostruct.rb:174:in method_missing': undefined method []' for nil:NilClass (NoMethodError) from test.rb:6:in `<main>' (referring to the line 'puts player.turn_num') — Yujun Wu
– Yujun Wu, Commented Nov 18, 2012 at 5:27

Zach Kemp · Accepted Answer · 2012-11-18 09:09:23Z

1

You don't need to initialize a Node inside Player, because any Player instance is already also a Node instance. Instead, you should pass the expected arguments into super:

class Player < Node
  def initialize(parent,&block)
    super(parent, :player, &block)
    self.turn_num = 1
  end
end

Generally, it's a bad idea to override .new - this is defined by default for all Ruby objects to allocate memory and then run the initialize method (if it exists). When you override it as self.new, you're just returning a bare Node instance, not a Player instance.

edited Nov 18, 2012 at 9:09

answered Nov 18, 2012 at 6:23

Zach Kemp

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