Overview
This article discusses Ruby modules.
What is a Module?
A mechanism for providing common methods and constants to classes and other modules.
# Module definition
module Hi
def say_hi
puts "Hi!"
end
end
Unlike classes, modules cannot be instantiated. They also cannot be inherited.
Modules can define class methods and instance methods.
Class methods cannot be called from the module's include target.
module Greet
# Class method of the module
def self.hi
puts "Hi!"
end
# Instance method of the module
def bye
puts "Bye!"
end
end
Greet.hi
class Speaker
include Greet
end
speaker = Speaker.new
speaker.bye # => Bye!
speaker.hi # => NoMethodError
Namespace
Modules can be used to create namespaces.
module University
class Student
def self.say
puts "I am a student"
end
end
end
class Student
def self.say
puts "I am a student"
end
end
Student.say # => I am a student
University::Student.say # => I am a student
Mixin
Mixins allow adding or overriding instance methods in classes without using inheritance.
While classes cannot inherit multiple times, multiple inheritance can be achieved through module mixins.
class Greet
include Hi
end
puts Greet.new.say_hi # => Hi!
It is worth noting that while Mixins and Traits are similar, Mixins use inheritance, whereas Traits can compose methods through various means other than inheritance, giving them a slightly different nuance.
cf. ja.wikipedia.org - Mixin
cf. ja.wikipedia.org - Trait
Adding Singleton Methods to Classes Using extend
You can add singleton methods to a class using extend.
module Hi
def hi
puts "Hi!"
end
end
class Greet; end
Greet.new.extend(Hi).hi # => Hi!
