Don'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 46 - Repeated Code Code Smell 11 - Subclassification for Code Reuse Code Smell 232 - Reusable Code 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 https://hackernoon.com/improving-the-code-one-line-at-a-time?embedable=true https://maximilianocontieri.com/refactoring-007-extract-class?embedable=true https://maximilianocontieri.com/refactoring-010-extract-method-object?embedable=true This article is part of the Refactoring Series. https://maximilianocontieri.com/how-to-improve-your-code-with-easy-refactorings?embedable=true Don't Repeat Yourself Don't Repeat Yourself TL;DR: How to remove repeated code TL;DR: How to remove repeated code Problems Addressed Don't Repeat Yourself Copy/Paste Programming No single source of truth Don't Repeat Yourself Copy/Paste Programming No single source of truth Related Code Smells Code Smell 46 - Repeated Code Code Smell 46 - Repeated Code Code Smell 11 - Subclassification for Code Reuse Code Smell 11 - Subclassification for Code Reuse Code Smell 232 - Reusable Code Code Smell 232 - Reusable Code 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 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) (This is the harder and not mechanical step) Sample Code (This is actual code generated by Google Gemini) (This is actual code generated by Google Gemini) See a complete explanation in this talk 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;
  }
} 

?> <?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)
}

?> <?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 [x] Semi-Automatic [x] 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 Coupling Related Refactorings https://hackernoon.com/improving-the-code-one-line-at-a-time?embedable=true https://hackernoon.com/improving-the-code-one-line-at-a-time?embedable=true https://maximilianocontieri.com/refactoring-007-extract-class?embedable=true https://maximilianocontieri.com/refactoring-007-extract-class?embedable=true https://maximilianocontieri.com/refactoring-010-extract-method-object?embedable=true https://maximilianocontieri.com/refactoring-010-extract-method-object?embedable=true This article is part of the Refactoring Series. https://maximilianocontieri.com/how-to-improve-your-code-with-easy-refactorings?embedable=true https://maximilianocontieri.com/how-to-improve-your-code-with-easy-refactorings?embedable=true

Walkthroughs, tutorials, guides, and tips. This story will teach you how to do something new or how to do something better.

Code Smell 255 - Addressing Parallel Hierarchies in Code

Clean Code With AI

Buy My Book

Refactoring 013 - Eliminating Repeated Code with DRY Principles

About Author

Comments

TOPICS

THIS ARTICLE WAS FEATURED IN

Related Stories

10 Predictions About the Future of Finance

106 Stories To Learn About Clean Code

100 Pieces of Programming Advice from the Book Clean Code by Robert Martin

110 Stories To Learn About Refactoring

3 Things Coding And Prose Writing Have In Common According To Cory House

4 Simple Habits For Engineering Teams To Beat Technical Debt

10 Predictions About the Future of Finance

106 Stories To Learn About Clean Code

100 Pieces of Programming Advice from the Book Clean Code by Robert Martin

110 Stories To Learn About Refactoring

3 Things Coding And Prose Writing Have In Common According To Cory House

4 Simple Habits For Engineering Teams To Beat Technical Debt

Light-Mode

Classic

Newspaper

Dark-Mode

Neon Noir

Minty

HN StartUps