Explanation of Modules

modules.rb

# Prerequisite explanations: String, Integer, Range, #puts, #rand

# This is how you create a module named Example:
module Example
end

# This is how you create methods in your module:
module Example
  def Example.a_method
    "i am a string"
  end

  def Example.another_method
    42
  end
end

# And you can call those methods:
Example.a_method
#=> "i am a string"

Example.another_method
#=> 42

# But if you changed your module name, all the methods would need to be renamed:
module AnotherExample
  def Example.a_method
    "i am a string"
  end

  def Example.another_method
    42
  end
end

AnotherExample.a_method
# NoMethodError: undefined method `a_method' for AnotherExample:Module

# It is better to use `self.a_method` instead of `Example.a_method` to avoid this brittleness:
module AnotherExample
  def self.a_method
    "i am a string"
  end

  def self.another_method
    42
  end
end

AnotherExample.a_method
#=> "i am a string"

# This works just as before because `self` refers to the module it is enclosed in:
module AnotherExample
  puts self
end
# AnotherExample

# Now we'll define a method called `roll` on a module called `Dice`:
module Dice
  def roll
    rand 1..6
  end
end

# Without a `self` in front of `roll` you can't call the method directly:
Dice.roll
# NoMethodError: undefined method `roll' for Dice:Module

# But you can use it in another module with `extend`:
module BoardGame
  extend Dice
end

BoardGame.roll
#=> 4