Refactoring Ruby: Extract Method

Extract Method can be used when you have several expressions, a code fragment, that can be grouped together. Even if there is one expression that could be better explained with a well thought out method name, it’s still a good move.

Let’s use Extract method on the Invoice#print method:

The method before refactoring looks like:

def print
  print_branding
  # print line items
  line_items.each do |line_item|
    puts "#{line_item.name}: #{line_item.price}"
  end
  # print subtotal
  puts "Subtotal: #{line_items.sum(&:price)}"
end

Often times, if you see comments explaining what a code fragment does, it’s a smell indicating there is a method to be extracted.

The method after refactoring looks like:

def print
  print_branding
  print_line_items
  print_subtotal
end

Let’s walk through the steps used when applying Extract Method:

1. Identify candidate fragments by looking for some common smells like, expressions that cluster together, comments explaining the intent, or if a good method name could add clarity.
2. Turn those fragments into a method whose name explains the purpose of the method.

Reach for this when a method contains groups of seemingly un-related code fragments, or when better naming will make it easier for you or your coworkers to understand the intent of code.