class Hamster::MutableHash

def self.[](pairs = {})
  MutableHash.new(Hash[pairs])
end

def delete(key)
  old_value = nil
  transform do |hash|
    old_value = hash.get(key)
    hash.delete(key)
  end
  old_value
end

def put(key, value = Undefined, &block)
  transform { |hash| hash.put(key, value, &block) }
end

def store(key, value)
  put(key, value)
  value
end