Working with legacy code

Pawel Pierzchala @zwrozka

We work with legacy code daily

We create legacy code daily

What is legacy code?

How to cope with legacy code?

The algorithm

• Find the code you want to fix
• Find the entry point
• Test it
• Fix it

How to find it?

How to test it?

How to fix it?

Or how to change spaghetti into ravioli?

Work in small steps

and add unit tests as you go

Start with naming the conditions

if roll % 2 != 0
  @won = true
end
          

winning_roll = roll % 2 != 0
if winning_roll
  @won = true
end
          

Extract methods

50.times do |i|
  @pop_questions.push "Pop Question #{i}"
  @science_questions.push "Science Question #{i}"
  @sports_questions.push "Sports Question #{i}"
end
          

def create_question(category, number)
  "#{category} Question #{number}"
end

50.times do |i|
  @pop_questions.push create_question("Pop", i)
  @science_questions.push create_question("Science", i)
  @sports_questions.push create_question("Sports", i)
end
          

Observe patterns

Similar prefixes?

Probably an object

puts "#{current_player_name} has #{current_player_purse} coins"
          

class Player < Struct.new(:name, :purse)
end
puts "#{current_player.name} has #{current_player.purse} coins"
          

Similar lists of arguments?

Probably an object

def is_winning?(purse, place)
def score(purse, place)
def has_won(name, purse, place)
          

class Player < Struct.new(:name, :purse, :place)

def is_winning?(player)
def score(player)
def has_won(player)
          

Avoid nightmare of integration

Don't create feature branch

Red Green Refactor?

Backlog

Exercise

Utility for renaming episodes

Usage

renamer.rb Seinfeld test result
          

renamer should accept its output files as input

Create an e2e test and speed it up with VCR

Links

Working Effectively With Legacy Code

Legacy Code Retreat