My favorite module methods pattern, and how it works with private

private_module_methods.rb

#!/usr/bin/env ruby

module M
  extend self

  def foo
    "hello world"
  end

  private

  def bar
    "private!"
  end
end

class C
  include M

  def baz
    "calling bar: #{bar}"
  end
end

puts M.foo
puts C.new.foo
puts C.new.baz

begin; puts M.bar;     rescue => ex; puts "Exception! => #{ex}"; end
begin; puts C.new.bar; rescue => ex; puts "Exception! => #{ex}"; end

results.txt

hello world
hello world
calling bar: private!
Exception! => private method `bar' called for M:Module
Exception! => private method `bar' called for #<C:0x2078f80>