Writing Module for Ruby

Question

How do you write a module for ruby. in python you can use

# module.py
def helloworld(name):
    print "Hello, %s" % name

# main.py
import module
module.helloworld("Jim")

Back to the Question how do you create a module in/for ruby

Answer 1

module NumberStuff 
  def NumberStuff.random 
    rand(1000000) 
  end 
end 

module LetterStuff 
  def LetterStuff.random 
    (rand(26) + 65).chr 
  end 
end 

puts NumberStuff.random 
puts LetterStuff.random

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Answer 2

Modules in Ruby have different purpose than modules in Python. Typically you use modules to define common methods that could be included in other class definition.

But modules in Ruby could also be used in similar way as in Python just to group methods in some namespace. So your example in Ruby would be (I name module as Module1 as Module is standard Ruby constant):

# module1.rb
module Module1
  def self.helloworld(name)
    puts "Hello, #{name}"
  end
end

# main.rb
require "module1"
Module1.helloworld("Jim")

But if you want to understand the basics of Ruby I would recommend to start with some quick guide to Ruby - StackOverflow is not the best way how to learn basics of new programming language :)

Answer 3

# meth.rb
def rat
  "rizzo"
end

# cla.rb
class Candy
  def melt
    "awwwww...."
  end
end

# main.rb
require 'meth'
require 'cla'
require 'mod'

puts rat
puts Candy.new.melt
puts Hairy.shave

In ruby, modules are the name for syntatic constructs used to group methods, constants, classes, and other modules. They're ruby's equivalent of namespaces.

A separate concept isgrouping by file, like above. Often, however, the two concepts coexist, with one file using a single module as its namespace.

# mod.rb
module Hairy
  def self.shave
    "ouch!"
  end
end

Answer 4

People have given some nice examples here but you can create and use modules in the following manner as well (Mixins)

Module to be included

#instance_methods.rb
module MyInstanceMethods
  def foo
    puts 'instance method foo called'
  end
end

Module to be extended

#class_methods.rb
module MyClassMethods
  def bar
    puts 'class method bar called'
  end
end

Included module methods act as if they are instance methods of the class in which the module is included

require 'instance_methods.rb'

class MyClass
  include MyInstanceMethods
end

my_obj = MyClass.new
my_obj.foo #prints instance method foo called
MyClass.foo #Results into error as method is an instance method, _not_ a class method.

Extended module methods act as if they are class methods of the class in which the module is included

require 'class_methods.rb'

class MyClass
  extend MyClassMethods
end

my_obj = MyClass.new
my_obj.bar #Results into error as method is a class method, _not_ an instance method.
MyClass.bar #prints class method bar called

You can even extend a module just for a specific object of class. For that purpose instead of extending the module inside the class, you do something like

my_obj.extend MyClassMethods

This way, only the my_object will have access to MyClassMethods module methods and not other instances of the class to which my_object belongs. Modules are very very powerful. You can learn ore about them using core API documentation

Please excuse if there are any silly mistakes in the code, I did not try it but I hope you get the idea.

Answer 5

Is it bad practice to include class definitions inside of a module? If yes, then what is the best way to create a class in a separate file and then include it in a different one?

Thanks.