Question

What is the way to extend a module function? In the following, I want to use B.foo

module A
    module_function
    def foo; end
end
module B
    extend A
end
B.foo

but it returns the error:

private method `foo' called for B:Module.

Answer 1

If you want to use it directly you need to make it public as well.

module A
  module_function
  public
  def hello
    puts "Hello"
  end
end

module B
  extend A
end


B.hello