Maxi ContieriDon't Repeat Yourself
TL;DR: How to remove repeated code
Problems Addressed
Don't Repeat Yourself
Copy/Paste Programming
No single source of truth
Related Code Smells
Code Smell 232 - Reusable Code
Maxi Contieri ・ Nov 25 '23
Context
Duplicated code is a severe code smell, it leads to maintainability problems and ripple effects.
Start by identifying behavior duplication.
Once you find it, you will extract it into reusable functions or classes, reducing redundancy, creating a single source of truth, and simplifying future updates.
Behavior duplication is a sign of a missing abstraction you need to create.
As always, you should search for it in the real world.
Refactoring isn't a one-time event; it's an ongoing process that should be integrated into your development workflow.
Steps
Make a contextual copy of the repeated code
Parametrize what is different
Invoke the abstraction
Find a real-world metaphor for the abstraction
(This is the harder and not mechanical step)
Sample Code
*(This is actual code generated by Google Gemini)
See a complete explanation in this talk*
Before
<?php
class AccessControlPanel {
private $users = [];
public function createRegularUser($username, $password, $email) {
$user = [
"username" => $username,
"email" => $email,
"type" => $this->regularUserRole(),
"creationDate" => $this->timeSource->currentTimestamp(),
"needsToChangePassword" = $this->needsToChangePassword(),
"loginPolicy" => $this->userLoginPolicy()
]
$this->users[] = $user;
$this->addCreationToJournal($user);
}
public function createAdminUser($username, $password, $email) {
$user = [
"username" => $username,
"email" => $email,
"type" => $this->regularUserRole(),
"creationDate" => $this->timeSource->currentTimestamp(),
"needsToChangePassword" = $this->needsToChangePassword(),
"loginPolicy" => $this->adminUserLoginPolicy()
]
$this->users[] = $user;
$this->addCreationToJournal($user);
return $user;
}
}
?>
After
<?php
class AccessControlPanel {
private $users = [];
// 1. Make a contextual copy of the repeated code
private function createUser(
$username,
$password,
$email,
$role,
$loginPolicy) {
$user = [
"username" => $username,
"email" => $email,
"type" => $role,
"creationDate" => $this->timeSource->currentTimestamp(),
"needsToChangePassword" => $this->needsToChangePassword(),
"loginPolicy" => $loginPolicy
];
$this->users[] = $user;
$this->addCreationToJournal($user);
return $user;
}
// 2. Parametrize what is different (in this case $role and $loginPolicy)
public function createRegularUser($username, $password, $email) {
// 3. Invoke the abstraction
return $this->createUser(
$username,
$password,
$email,
$this->regularUserRole(),
$this->userLoginPolicy());
}
public function createAdminUser($username, $password, $email) {
return $this->createUser(
$username,
$password,
$email,
$this->adminUserRole(),
$this->adminUserLoginPolicy());
}
// 4. Find a real-world metaphor for the abstraction
// private function createUser(
// $username,
// $password,
// $email,
// $role,
// $loginPolicy)
}
?>
Type
[X] Semi-Automatic
The steps are defined but sometimes not about text duplication, but behavior duplication.
Safety
Since this is not a mechanical refactoring, you need good coverage on the code you modify.
Why is the code better?
You have a single source of truth, more compact code, and an easier-to-maintain solution.
Tags
- Coupling
Related Refactorings
Credits
Imagen de Rachealmarie en Pixabay
This article is part of the Refactoring Series.
