Aspects of Module included callback

gistfile1.rb

# supporting the answer for http://stackoverflow.com/questions/11742890/merge-two-ruby-modules-but-not-include/12036994#12036994

module A
  def a
    puts "a"
  end
end

module B
  # note 'self.' part here, which makes method a module method
  def self.included(base)
    puts "B.included"
    base.send(:include, A)
  end
end

puts "For C1"
class C1
  puts "before include B"
  include B
  puts "after include B"
end

puts "C1.new.a"
C1.new.a

# Output:
#
# For C1
# before include B
# B.included
# after include B
# C1.new.a
# a


puts
puts "For M"
module M
  puts "before include B"
  include B
  puts "after include B"
end

# Output:
# For M
# before include B
# B.included
# after include B

puts
puts "For C2"
class C2
  puts "before include M"
  include M
  puts "after include M"
end

puts "C2.new.a"
C2.new.a

# Output:
# For C2
# before include M
# after include M
# C2.new.a
# a

class C3
end

puts
puts "For C3"
c3 = C3.new
puts "before c3.extend B"
c3.extend(B)
puts "after c3.extend B"
c3.a rescue puts "Exception: ", $!.inspect

# Output:
# For C3
# before c3.extend B
# after c3.extend B
# Exception: 
# #<NoMethodError: undefined method `a' for #<C3:0x100168360>>

puts
puts "before c3.extend M"
c3.extend(M)
puts "after c3.extend M"
puts "c3.a"
c3.a

# Output:
# before c3.extend M
# after c3.extend M
# c3.a
# a