RubyGuides
Share this post!

Introduction to Refactoring

If you aren’t familiar with the term, refactoring is the act of improving the quality of code without changing what it does. This will make your code a lot easier to work with. In this post you will learn some common refactoring techniques, let’s get started!

Extract Method

One of the most common refactorings is the one known as ‘extract method’. In this refactoring you move some code from an old method into a new method. This will allow you to have smaller methods with descriptive names.

Let’s take a look at an example:

@sold_items = %w( onions garlic potatoes )

def print_report
  puts "*** Sales Report for #{Time.new.strftime("%d/%m/%Y")} ***"
  @sold_items.each { |i| puts i }
  puts "*** End of Sales Report ***"
end

We can start by extracting the ugliest part of this method, the current date generation.

def print_report
  puts "*** Sales Report for #{current_date} ***"
  @sold_items.each { |i| puts i }
  puts "*** End of Sales Report ***"
end

def current_date
  Time.new.strftime("%d/%m/%Y")
end

This already reads better, but we can go a bit further. Let’s extract a few more methods to end up with this code:

def print_report
  print_header
  print_items
  print_footer
end

def print_header
  puts "*** Sales Report for #{current_date} ***"
end

def current_date
  Time.new.strftime("%d/%m/%Y")
end

def print_items
  @sold_items.each { |i| puts i }
end

def print_footer
  puts "*** End of Sales Report ***"
end

Yes, the code is longer now, but isn’t this easier to read? Don’t be afraid of small methods, they are good for your code.

Refactoring Conditionals

You can also refactor complicated conditionals into methods to make them more readable.

Example:

def check_temperature
  if temperature > 30 && (Time.now.hour >= 9 && Time.now.hour <= 17)
    air_conditioner.enable!
  end
end

The second part of this if statement is not super-readable, so let's extract it into a method:

def check_temperature
  if temperature > 30 && working_hours
    air_conditioner.enable!
  end
end

def working_hours
  Time.now.hour >= 9 && Time.now.hour <= 17
end

What we have done here is to give our condition a descriptive name, which makes things a lot easier for future readers of this code (including you!).

Replace Method with Method Object

Sometimes you have a big method that got out of control. In this case it might be hard to refactor because big methods tend to have many local variables. One solution is to use the 'Method Object' refactoring.

"Big methods are where classes go to hide." - Uncle Bob

Let's see an example:

require 'socket'

class MailSender
  def initialize
    @sent_messages = []
  end

  def send_message(msg, recipient = "blackbytes.info")
    raise ArgumentError, "message too small" if msg.size < 5

    formatted_msg = "[New Message] #{msg}"

    TCPSocket.open(recipient, 80) do |socket|
      socket.write(formatted_msg)
    end

    @sent_messages << [msg, recipient]

    puts "Message sent."
  end
end

sender = MailSender.new
sender.send_message("testing")

To perform the refactoring we can create a new class and promote the local variables into instance variables. This will allow us to further refactor this code without having to worry about passing data around.

Hey! Want to improve your Ruby skills in a big way? Check out my New Ruby Course 🙂

This is the MailSender class after the refactoring:

class MailSender
  def initialize
    @sent_messages = []
  end

  def deliver_message(message)
    send(message)
    @sent_messages << message
    puts "Message sent."
  end

  def send(msg)
    TCPSocket.open(msg.recipient, 80) { |socket| socket.write(msg.formatted_msg) }
  end
end

And this is the new class we introduced:

class Message
  attr_reader :msg, :recipient

  def initialize(msg, recipient = "blackbytes.info")
    raise ArgumentError, "message too small" if msg.size < 5

    @msg       = msg
    @recipient = recipient
  end

  def formatted_msg
    "[New Message] #{msg}"
  end
end

sender = MailSender.new
msg    = Message.new("testing")

sender.deliver_message(msg)

Conclusion

Using these refactoring techniques will help you adhere to the Single Responsibility Principle and keep your classes and methods under control.

If you enjoyed this article please share it with your friends so they can enjoy it too 🙂