Ruby attr_accessor not being read

Question

I am developing a game with Ruby using the Gosu and Chipmunk gems. I have the following class in the file named HeroBullets.rb:

require 'gosu'

class HeroBullets
  attr_accessor :y
  def initialize(window)
    @x = 20
    @y = 0
  end
end

I know need to access this class from another file, Physics.rb which handles all the Chipmunk code.

At the top I have:

require 'chipmunk'

load 'HeroBullets.rb'

class Physics
   attr_accessor :play_area 

def initialize(window)

    @hBullets = Array.new(25)
    @hBullets << HeroBullets.new(window)
    @hBullets << HeroBullets.new(window)
end

And further down there is:

  def fire_arrow(y)
    for i in 0...@hBullets.count
      @bullet = @hBullets[i]
      if(@bullet.y == y)
        @hBullets[i].active = true
      end
    end
  end

The Error I get is:

Physics.rb:112:in block in fire_arrow': undefined methody' for nil:NilClass 
(NoMethodError) from Physics.rb:110:in each' from Physics.rb:110:infire_arrow'
from FileManager.rb:90:in fireHero' from .../lib/main.rb:90:inupdate' from .../lib/main.rb:129:in `'

Answer 1

The problem is that if @hBullets has 10 elements, @hBullets.count will output 10, but @hBullets[10] does not work, because the index of an array starts at 0 not at 1. The tenth element will be in @hBullets[9]. You get the error message because the element you are trying to access is nil, not because "attr_accessor is not being read".

That being said, Ruby offers much easier ways to iterate over an array. I would rewrite your code like this:

def fire_arrow(y)
  @hBullets.each do |bullet|
    bullet.active = true if bullet.y == y
  end
end

Another problem with your code is that you initialize a new array like this:

@hBullets = Array.new(25)

This creates an array with 25 elements that are all nil. You should start with an empty array instead:

@hBullets = Array.new

Or:

@hBullets = []