Ruby gotcha

gotcha.rb

class User
  DEFAULT_VALUES = {:name => "--",
                    :roles => [],
                    :username => "abc123"
                   }

  ROLE = ["developer", "user", "designer", "admin"]

  attr_accessor :name, :username, :roles

  def initialize(values)
    new_vals = DEFAULT_VALUES.merge(values)
    self.name = new_vals[:name]
    self.roles = new_vals[:roles]
    self.username = new_vals[:username]
  end

  def add_role(role)
    self.roles << role
  end
end

ralph = User.new(name: "Ralph", username: "ralph1234")
bob = User.new(name: "Bob", username: "bob")
ralph.add_role("developer")
ralph.add_role("admin")
bob.add_role("user")