Refactoring Ruby: Extract Method

Jon Lunsford
1 min readSep 3, 2018

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.

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Jon Lunsford

Engineer @convertkit, programming enthusiast, father, and musician