Question

The variable value in the initialize method of LocationList is populated in line 014. These changes are relected by the print statement in line 015, but the return in line 016 thinks the hash is still empty (scroll right to see return value after =>).

def random_point
  x = rand * 2.0 - 1.0
  y = rand * 2.0 - 1.0
  until x**2 + y**2 < 1.0
    x = rand * 2.0 - 1.0
    y = rand * 2.0 - 1.0
  end
  return [x, y]
end

class LocationList < Hash
  def initialize(node_list)
    value = {}
    node_list.each {|node| value[node] = random_point }
    print value
    return value
  end
end

z = ["moo", "goo", "gai", "pan"]

LocationList.new(z)
#=> {"moo"=>[0.17733298257484997, 0.39221824315332987], "goo"=>[-0.907202436634851, 0.3589265999520428], "gai"=>[0.3910479677151635, 0.5624531973759821], "pan"=>[-0.37544369339427974, -0.7603500269538608]}=> {}

Doing substantially the same thing in a global function yields the intended return value:

def foo(node_list)
  value = {}
  node_list.each {|node| value[node] = random_point }
  return value
end

foo(z)
#=> {"moo"=>[-0.33410735869573926, -0.4087709899603238], "goo"=>[0.6093966465651919, 0.6349767372996336], "gai"=>[0.718925625951371, -0.6726652512124924], "pan"=>[0.08604969147566277, -0.518636160280254]}

Answer 1

You’re creating a new Hash that you call value in your initialize method, rather than initializing self. Illustrating this inline:

class LocationList < Hash
  def initialize(node_list)
    # self is already a LocationList, which is a Hash

    value={}
    # value is now a new Hash

    node_list.each {|node| value[node]=random_point}
    # value now has keys set

    return value
    # value is now discarded
    # LocationList.new returns the constructed object; it does not return
    # the result of LocationList#initialize
  end
end

Try this instead:

class LocationList < Hash
  def initialize(node_list)
    node_list.each {|node| self[node]=random_point}
  end
end