prepend_vs_alias.rb

#!/usr/bin/env ruby

class A
  def b
    'b'
  end
end

module X
  def b
    "#{super}x"
  end
end

module Y
  def self.included base
    base.class_eval do
      alias_method :b_without_y, :b
      alias_method :b, :b_with_y
    end
  end

  def b_with_y
    "#{b_without_y}y"
  end
end

case ARGV[0]
when '--prepend' # bx
  A.prepend X
when '--alias'   # by
  A.include Y
when '--both'    # SystemStackError
  A.prepend X
  A.include Y
when '--flip'    # byx
  A.include Y
  A.prepend X
end

puts A.new.b