Nested Hash with Database

nested_hash_example.rb

module MockRetriever
  def self.fetch_rows database, table
    return ["#{rand(100)} Main St.", "#{rand(100)} Second Ave.", "#{rand(100)} Peach Ln."]
  end
end

module AddressHandler
  # @addresses = Hash.new( {} )   # old code - returns the SAME hash, not a new hash
  @addresses = Hash.new { |hash, key| hash[key] = {} }

  def self.addresses state, city
    if value = @addresses[state][city]
      puts "fetched stored value"
      value
    else
      puts "storing new value"
      @addresses[state][city] = MockRetriever.fetch_rows state, city
    end
  end
end

if __FILE__ == $0 
  p AddressHandler.addresses 'alaska', 'anchorage'
  p AddressHandler.addresses 'washington', 'vancouver'
  p AddressHandler.addresses 'british columbia', 'vancouver'
  p AddressHandler.addresses 'washington', 'vancouver'
end

With @addresses = Hash.new( {} ):

storing new value
["7 Main St.", "48 Second Ave.", "31 Peach Ln."]
storing new value
["98 Main St.", "87 Second Ave.", "39 Peach Ln."]
fetched stored value
["98 Main St.", "87 Second Ave.", "39 Peach Ln."]
fetched stored value
["98 Main St.", "87 Second Ave.", "39 Peach Ln."]

With @addresses = Hash.new { |hash, key| hash[key] = {} }

storing new value
["67 Main St.", "76 Second Ave.", "76 Peach Ln."]
storing new value
["67 Main St.", "8 Second Ave.", "8 Peach Ln."]
storing new value
["98 Main St.", "55 Second Ave.", "98 Peach Ln."]
fetched stored value
["67 Main St.", "8 Second Ave.", "8 Peach Ln."]

The latter is the desired behavior.