Ruby inheritance nil class

Question

I'm trying to make a game but I am having problems settinga default value for an attribute and having a different default value for each subclass.

Here is the problem:

class Player
   attr_accessor :hp 
   @hp = 2
end

class Harper < Player
  @hp = 5
end

bill = Harper.new.hp #=>nil

I'm expecting Harper.new.hp to be 5 but it's showing nil instead, and I don't understand why.

Answer 1

The problem with your initialization is that it exists at the class level. That is, you are creating a class instance variable (confusing?) not an object-instance variable as you expect.

In order to create an instance variable you need to do it in a method run at the instance level, like the initialize method which runs when you create an object with the "new" method.

Example:

class Hello
  @world = "World!"
  def initialize
    @to_be_or_not_to_be = "be!"
  end
end
=> :initialize

inst = Hello.new
inst.instance_variables
=> [:@to_be_or_not_to_be]

Hello.instance_variables
=> [:@world]

inst.class.instance_variables
=> [:@world]

Answer 2

You need to place your assignments on an initialize function:

class Player
  attr_accessor :hp 
  def initialize
    @hp = 2
  end
end

class Harper < Player
  def initialize
    super  ## May not be necessary for now.
    @hp = 5
  end
end

bill = Harper.new.hp
# => 5

Answer 3

new class method runs instance method initialize , so your code should look like:

class Harper < Player
  def initialize
    @hp = 5
  end
end