I have been trying to clean up some old code with Ruby modules. This post is to help me remember the differences between include and extend in Ruby.

class Foo
  extend ActionView::Helpers::NumberHelper
end

module Foo
  extend ActionView::Helpers::NumberHelper
end

Foo.number_to_currency 2
 => "$2.00"

class Foo
  include ActionView::Helpers::NumberHelper
end

foo = Foo.new
foo.number_to_currency 2
 => "$2.00"