My employer, Razoo, treated its developers to RailsConf 2010 this year. Very late the second night of the conference (the first night I was there–we skipped the tutorials), I saw Yehuda Katz give an impromptu Birds of a Feather talk about upcoming changes in Rails. It was good, but the thing I remember most clearly was his explanation of
extend in Ruby. He let code do the explaining:
# a module with a method module Says def hello puts 'hello' end end # a class we want to have the method (not an instance; the class) class Person end # (our end goal) class Person def self.hello puts 'hello' end end # there are two ways to achieve this # using extend class Person extend Says end # or using include class Person class << self include Says end end
So, in short, include just includes the module’s methods as instance methods and extend includes the module’s methods as class methods. I always do better with examples than reading technical documentation!