Constant resolution in Ruby (http://valve.github.io/blog/2013/10/26/constant-resolution-in-ruby/)

example.rb

module Foo
  A = 1
  B = 2

  def a1
    A
  end

  def b1
    B
  end
end

module Bar
  A = 3
  B = 4

  def a2
    A
  end

  def b2
    B
  end
end

class Test
  include Foo
  include Bar
end

p Test.constants # => [:A, :B]
p Test.new.a1 # => 1
p Test.new.b1 # => 2
p Test.new.a2 # => 3
p Test.new.b2 # => 4