My solution to Sandi Metz and Katrina Owen's 99 Bottles of OOP problem

bottles.rb

class Bottles
  def song
    verses 99, 0
  end

  def verses high, low
    high.downto(low).map { |count| verse count }.join "\n"
  end

  def verse count
    bottles = Hash.new { |hash, key| "#{key} bottles" }
    bottles[6] = '1 six-pack'
    bottles[1] = '1 bottle'
    bottles[0] = 'no more bottles'

    actions = Hash.new 'Take one down and pass it around'
    actions[1] = 'Take it down and pass it around'
    actions[0] = 'Go to the store and buy some more'

    remaining = count > 0 ? count - 1 : 99

    <<-VERSE                                                                                                                                                                 
#{bottles[count].capitalize} of beer on the wall, #{bottles[count]} of beer.                                                                                                 
#{actions[count]}, #{bottles[remaining]} of beer on the wall.                                                                                                                
VERSE                                                                                                                                                                        
  end
end

Replacing "6 bottles" with "1 six-pack" only requires adding a single line of code...

bottles[6] = '1 six-pack'

Updating this with a minimal refactoring and the addition of the six-pack feature.