bang_methods.rb

class JustMerging
  def self.updates_object(passed_in_hash)
    passed_in_hash.merge!(add_this: "YAY")
    return
  end
end

class WeHaveAHash
  def self.creating_a_hash
    my_great_hash = {super_cool: true, wow: "what a great hash"}
    JustMerging.updates_object(my_great_hash)
    my_great_hash
  end
end

result = WeHaveAHash.creating_a_hash
puts result
# {:super_cool=>true, :wow=>"what a great hash", :add_this=>"YAY"}