This document outlines the principles and structure of a legacy coderetreat event. The retreat focuses on practicing legacy code techniques through pair programming on an existing codebase. Participants work through 6 sessions over 1 day, each focusing on a different technique like code reading, adding system tests, encapsulating dependencies, and refactoring conditionals and functions. The goal is to experiment, learn, and have fun while extending coding skills and comfort with legacy code.

1. Legacy Coderetreat

2. About
Coderetreat started in 2009, created by:
• Gary Bernhardt
• Patrick Welsh
• Nayan Hajratwala
• Corey Haines
Legacy code retreat created in 2012 by JB
Rainsberger

3. Me
Adrian Bolboaca
Technical and Organizational Trainer and Coach at Mozaic Works

4. Why
Practice
Experiment
Learn legacy code techniques
Extend your comfort zone
Learn through pair-programing
Have fun

5. How
1 Day of coding
Have an existing codebase
6 pairing partners
On average 135 minutes of coding
6 different legacy code techniques
A lot of fun!

6. Day structure
Introduction
3 sessions in the morning
Lunch 1h
3 sessions in the afternoon
Day retrospective 30 minutes

7. Principles
Language agnostic
Follow the constraints of the session
Delete the code changes after each session
Focus on practice
Experiment each session
Have fun!

8. Prerequisites
Computer
Coding environment
Testing environment
Local source control (git, etc)

9. The four elements of simple design
1. Passes its tests
2. Minimizes duplication
3. Maximizes clarity
4. Has fewer elements

10. Basic rules of refactoring
Steps
1. Duplicate implementation
2. Cover duplicated implementation with tests
(these are learning tests)
3. Reroute original code to new code
(make sure you have some initial tests)
4. Remove old implementation
5. Check tests pass

11. Git
cd /myroot/myfolder
git clone https://github.com/jbrains/trivia.git
git status -> check pending changes
git commit -am "non-empty message"
git reset --hard HEAD --> reset to last commit
git clean -f -d -x -> delete all untracked files

12. Codebase
You can find it at https://github.com/jbrains/trivia
Use git to clone the repository

13. Session 1: Code reading
Take 30 minutes to read the code
Try to understand it
Work in pairs

14. Session 2: From nothing to system
tests
1.Find an entry point into your system, a method at
the highest level possible, closest to external calls
or the user interface
2. Define a limit of your system that blocks you
from verifying resulting behavior
3. Find a way to fake this limit so that you can
catch the results
4. Write a system test that verifies one of your
assumptions about one specific behavior of that
method
5. Refactor

15. Session 3: Encapsulate external
dependencies
1. Look for a method that uses an external dependency (IO, framework,
hardware, etc)
2. Isolate the real call to the external dependency from the rest of the
method logic, so that this only uses the result/value of the external call
3. Extract the real call to the external dependency into a separate method
4. Extract the method to a new class
5. Create an abstraction for the class
6. Dependency inject the abstraction by:
a. Constructor
b. Property
c. Parameter
7. Rewrite your tests so that the external dependency is:
a. stubbed
b. mocked

16. Lunch
1 hour

17. Session 4: Reveal intent
Concepts
1. Find magic number/string within the code
2. Replace the number/string with a symbolic constant which encapsulated the
value and describes the meaning of the number/string
1. Find a variable/method/class with a non-descriptive name, like Foo
2. Change Foo variable/method/class to a meaningful explicit name which
might be too long to be useful but reveals intent
3. Iteratively improve* the variable/method/class name.
Improving means:
● Shortening towards a more comfortable length
● Keeping the explicit nature of the name intact
● Staying coherent with the domain
● Avoiding duplication of concepts, i.e. synonyms for the same concept

18. Session 5: Refactoring conditionals
(slide 1/2)
Concepts
● Guard Clauses [1]
Is a chunk of code at the top of a function that serves
a similar purpose to a Precondition. It typically does
one (or any or all) of the following:
a. Returns an error when invalid input parameters.
b. Bails out when function call is inappropriate.
c. Handle trivial cases quickly.
● Explaining Variable [2]
Transform an expression into a temporary variable
that explains the purpose of the logical expression

19. Session 5: Refactoring conditionals
(slide 2/2)
Concepts
● Decompose Conditional [4]
1. Find a method that contains a conditional expression and a chunk of
functionality within this conditional
2. Use extract method to move the real functionality into a separate method
● Consolidate Conditional Expression [5]
1. Find a method that contains multiple conditional expressions or a
composite conditional
2. Use extract method to move all of the conditional logic into a separate
method so that it combines all the conditional logic
3. Give the new method a descriptive name that you can use in the
original method (like an explaining variable)

20. Session 6: Extract pure functions
A pure function always evaluates the same result value given the same argument
value(s). Its result cannot depend on any hidden information or state that may change
as program execution proceeds or between different executions of the program. *
Steps
1. Find an atomic piece of code that can be moved into a separate public function
by using Extract method
2. Replace all external dependencies within this function with independent or primitive
parameters
a. Constants
b. Class variables
c. Global variables
d. Method variables outside of the extracted code
3. Returns an object instantiated inside the function
4. Add tests for the method
a. At least one test for each parameter
b. One test for each value range of each parameter
5. Refactor

21. Closing circle
1)How did you feel
2)What did you learn
3)What would you apply Monday?

22. Contact me
Remote pair-programming
Unit testing workshop
Test driven development workshop
Refactoring workshop
Working FAST and safe with existing code workshop
Code retreat workshop
http://mozaicworks.com
adrian.bolboaca@mozaicworks.com
@adibolb
blog.adrianbolboaca.ro