Extending a Ruby module in another module, including the module methods

Question

Whenever I try to extend a ruby module, I lose the module methods. Neither include nor extend will do this. Consider the snippet:

module A 
  def self.say_hi
    puts "hi"
  end
end

module B 
  include A
end

B.say_hi  #undefined_method

Whether B Includes or Extends A, say_hi will not be defined.

Is there any way to accomplish something like this?

Answer 1

If you are the author of module A and will frequently need this, you can re-author A like so:

module A 
  module ClassMethods
    def say_hi
      puts "hi"
    end
  end
  extend ClassMethods
  def self.included( other )
    other.extend( ClassMethods )
  end
end

module B 
  include A
end

A.say_hi #=> "hi"
B.say_hi #=> "hi" 

Answer 2

I don't think there's any simple way to do it.

So here is a complex way:

module B
  class << self
    A.singleton_methods.each do |m|
      define_method m, A.method(m).to_proc
    end
  end
end

You can put it in a helper method like this:

class Module
  def include_module_methods(mod)
    mod.singleton_methods.each do |m|
      (class << self; self; end).send :define_method, m, mod.method(m).to_proc
    end
  end
end

module B
  include_module_methods A
end