class String
  ALPHABET = ('a'..'z').to_a
  VOWELS = %w(a e i o u)
  CONSONANTS = ALPHABET - VOWELS

  def namna_sub
    case self
    when '?'
      ALPHABET.sample
    when '*'
      VOWELS.sample
    when '#'
      CONSONANTS.sample
    else
      self
    end
  end
end