ruby, do I need to include the inheritance each time I open a class? Answer: NO (but the inheritance must be there the 1st time or you'll get a superclass mismatch TypeError)

opening_an_inherited_class.rb

# [be careful, though, if you switch the order of introduction, then you will get this error:
# <file>.rb:11:in `<main>': superclass mismatch for class Dog (TypeError)
class Dog < Hash
  def silly(key)
    self[key] = 88 + key.to_i
  end
end

# This is the *key* point: we can re-open this class and it won't give us any trouble!
class Dog
  def workable(h)
    puts "HI: #{h}"
    p self.keys
    puts "WORD!"
  end
end

dog = Dog[key: 'val']
p dog
dog.silly(7)
dog.workable(4)
p dog
dog.workable(9)

# output (ruby 2.1.2)
{:key=>"val"}
HI: 4
[:key, 7]
WORD!
{:key=>"val", 7=>95}
HI: 9
[:key, 7]
WORD!