Refactoring Legacy Code

Pablo Machadomachadoum@gmail.com

Legacy Code?

Code written using old technology?

Code written by somebody who doesn't work for the company anymore?

A code very fragile or complicated?

Legacy Code

➔ Hard to understand and maintain

➔ Intimidating to be changed

Legacy Code?

“To me, legacy code is simply code without tests.”Michael Feathers

Legacy Code?

“If you wrote a new feature today, which took you a lot of mental energy and time, and tomorrow you'll be afraid to change it …”

Refactoring?

Why Refactor?

➔ To understand the code

➔ To improve the health of code-base

➔ To be confident

➔ To optimize for readability

Why Refactor?

➔ To understand the code

➔ To improve the health of code-base

➔ To be confident

➔ To optimize for readability

The Fear Factor

Unit Test

Characterization tests

Refactor Dilemma

When we refactor, we should have tests.

To test we often have to refactor.

Legacy Code Change

Identify Change Points

Identify Test Points

Break Dependecies

Write Test

Refactor

Working Effectively With

Legacy Code

Working Effectively With

Legacy Code

Baby Steps

Working Effectively With

Legacy Code

Invest only where necessary

Working Effectively With

Legacy Code

Know how to use the tools

Breaking Dependencies

External Dependencies

Production Code

External Dependencies

Production Code

Test Code

External Dependencies

Test Code

Production Code

Internal/Hidden

dependencies

Production Code Refactor To Test

Test Code

Production Code Test Code

Internal/Hidden

dependencies

Refactor Technique

Sprout Method

When?Add a feature as completely new code in a untestable method.

How?Identify the inputs and outputs of the new methodCreate a call for the new methodDevelop the new method with TDD

Sprout Method

AdvantagesTest new codeSepareta new cold from the old

DisadvantagesDont test old codeDont make the code better

Wrap Class

When?Add a feature as completely new code in complex class.

How?Create a class and extend the old classOverride the old method and make a callDevelop the new method with TDD

Sprout Method

AdvantagesTest new codeSepareta new cold from the old

DisadvantagesDont test old codeDont make the code better

Referências

http://refactoring.com/