creating key/value hash out of array in ruby

Question

I came across an old piece of code which was creating the hash datatype using simple arrays in ruby. I get most of it, except one part:

The point as I understand it is, every element of @store is a memory location for a particular key/value pair, as a function of the key. So @store[3] would generally store key/value pairs corresponding to key=3, key=53, ... and in general where key % size == 3 (in this case size = 50).

However, when I set hash[3] = 7 , hash[53] = 9 , etc., every element of @store array is populated with the key/value pairs, and not just the index 3 element. It seems like the line @store[store_key] << [key, value] in the method []=(key, value) is adding [key, value] to every element of @store , and not just one with the index store_key . Any ideas?

class SimpleHash
  attr_accessor :size, :store

  def initialize(size)
    @size = size
    @store = Array.new(size, [])
  end

  def []=(key, value)
    store_key = key % @size
    index = find_key(key, @store[store_key])
    if index
      @store[store_key][index][1] = value
    else
      p "***********************************"
      p @store
      @store[store_key] << [key, value]
      p "after"
      p store_key
      p @store
    end
  end
end

hash = SimpleHash.new(50)
p hash
hash[3] = 5
p hash
hash[3] = 7
hash[53] = 9
hash[103] = 11
hash[104] = 11

Answer 1

Although your question's a bit unclear, I can guess what the problem is.

@store = Array.new(size, [])

That creates an array of the right size, but where every element is the SAME OBJECT.

Change the array-within-an-array at any position, and the change will be evident in every position.

Try instead

@store = Array.new
size.times { @store << [] }

Every sub-array will be a separate object that way.

EDIT

@nafaa boutefer's answer is better. The block gets evaluated for each instance of the array so each sub-array is a different object.

@store = Array.new(size){ [] }

Answer 2

You can simply do this

@store = Array.new(size){ [] }

Every element is a separate array.