Don't Repeat Yourself
TL;DR: How to remove repeated code
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Don't Repeat Yourself
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Copy/Paste Programming
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No single source of truth
Code Smell 11 - Subclassification for Code Reuse
Code Smell 232 - Reusable Code
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.
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Make a contextual copy of the repeated code
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Parametrize what is different
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Invoke the abstraction
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Find a real-world metaphor for the abstraction
(This is the harder and not mechanical step)
(This is actual code generated by Google Gemini)
See a complete explanation in this talk
<?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;
}
}
?>
<?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)
}
?>
[X] Semi-Automatic
The steps are defined but sometimes not about text duplication, but behavior duplication.
Since this is not a mechanical refactoring, you need good coverage on the code you modify.
You have a single source of truth, more compact code, and an easier-to-maintain solution.
- Coupling
Refactoring 002 - Extract Method
Refactoring 003 - Extract Constant
Refactoring 007 - Extract Class
Refactoring 010 - Extract Method Object
Image from Rachealmarie on Pixabay
This article is part of the Refactoring Series.