Welcome to the very first lesson of the "Clean Code with Multiple Classes in PHP" course! 🎉 This course aims to guide you in writing code that's easy to understand, maintain, and enhance. Within the broader scope of clean coding, effective class collaboration is crucial for building well-structured applications. In this lesson, we will delve into the intricacies of class collaboration and coupling — key factors that can make or break the maintainability of your software. Specifically, we'll address some common "code smells" that indicate problems in class interactions and explore ways to resolve them.
Let's dive into the challenges of class collaboration by focusing on four common code smells:
- Feature Envy: Occurs when a method in one class is overly interested in methods or data in another class.
- Inappropriate Intimacy: Describes a situation where two classes are too closely interconnected, sharing private details.
- Message Chains: Refers to sequences of method calls across several objects, indicating a lack of clear abstraction.
- Middle Man: Exists when a class mainly delegates its behavior to another class without adding functionality.
Understanding these code smells will enable you to improve your class designs, resulting in cleaner and more maintainable code.
These code smells can significantly impact system design and maintainability. Let's consider their implications:
- They can lead to tightly coupled classes, making them difficult to modify or extend. 🔧
- Code readability decreases as it becomes unclear which class is responsible for which functionality.
Addressing these issues often results in code that's not only easier to read but also more flexible and scalable. Tackling these problems can markedly enhance software architecture, making it more robust and adaptable.
Feature Envy occurs when a method in one class is more interested in the properties or methods of another class than its own. Here's an example:
php1class ShoppingCart { 2 private $items = []; 3 4 public function calculateTotalPrice() { 5 $total = 0; 6 foreach ($this->items as $item) { 7 $total += $item->getPrice() * $item->getQuantity(); 8 } 9 return $total; 10 } 11} 12 13class Item { 14 private $price; 15 private $quantity; 16 17 public function __construct($price, $quantity) { 18 $this->price = $price; 19 $this->quantity = $quantity; 20 } 21 22 public function getPrice() { 23 return $this->price; 24 } 25 26 public function getQuantity() { 27 return $this->quantity; 28 } 29}
In this scenario, calculateTotalPrice() in ShoppingCart overly accesses data from Item, indicating feature envy.
To refactor, consider moving the logic to the Item class:
php1class ShoppingCart { 2 private $items = []; 3 4 public function calculateTotalPrice() { 5 $total = 0; 6 foreach ($this->items as $item) { 7 $total += $item->calculateTotal(); 8 } 9 return $total; 10 } 11} 12 13class Item { 14 private $price; 15 private $quantity; 16 17 public function __construct($price, $quantity) { 18 $this->price = $price; 19 $this->quantity = $quantity; 20 } 21 22 public function calculateTotal() { 23 return $this->price * $this->quantity; 24 } 25}
Now, each Item calculates its own total, reducing dependency and distributing responsibility appropriately. ✔️
Inappropriate Intimacy occurs when a class is overly dependent on the internal details of another class. Here's an example:
php1class Library { 2 private $book; 3 4 public function setBook(Book $book) { 5 $this->book = $book; 6 } 7 8 public function printBookDetails() { 9 echo "Title: " . $this->book->getTitle(); 10 echo "\nAuthor: " . $this->book->getAuthor(); 11 } 12} 13 14class Book { 15 private $title; 16 private $author; 17 18 public function __construct($title, $author) { 19 $this->title = $title; 20 $this->author = $author; 21 } 22 23 public function getTitle() { 24 return $this->title; 25 } 26 27 public function getAuthor() { 28 return $this->author; 29 } 30}
In this scenario, the Library class relies too heavily on the details of the Book class, demonstrating inappropriate intimacy. The key distinction between Inappropriate Intimacy and Feature Envy is that inappropriate intimacy involves a significant intertwining between two classes, while feature envy is about a method's excessive interest in another class's data or behavior instead of its own.
To refactor, allow the Book class to handle its own representation:
php1class Library { 2 private $book; 3 4 public function setBook(Book $book) { 5 $this->book = $book; 6 } 7 8 public function printBookDetails() { 9 echo $this->book->getDetails(); 10 } 11} 12 13class Book { 14 private $title; 15 private $author; 16 17 public function __construct($title, $author) { 18 $this->title = $title; 19 $this->author = $author; 20 } 21 22 public function getDetails() { 23 return "Title: " . $this->title . "\nAuthor: " . $this->author; 24 } 25}
This adjustment enables Book to encapsulate its own details, encouraging better encapsulation and separation of concerns. 🛡️
Message Chains occur when classes need to traverse multiple objects to access the methods they require. Here's a demonstration:
php1class User { 2 private $address; 3 4 public function setAddress(Address $address) { 5 $this->address = $address; 6 } 7 8 public function getAddress() { 9 return $this->address; 10 } 11} 12 13class Address { 14 private $zipCode; 15 16 public function setZipCode(ZipCode $zipCode) { 17 $this->zipCode = $zipCode; 18 } 19 20 public function getZipCode() { 21 return $this->zipCode; 22 } 23} 24 25class ZipCode { 26 public function getPostalCode() { 27 return "90210"; 28 } 29} 30 31// Usage 32$user = new User(); 33echo $user->getAddress()->getZipCode()->getPostalCode();
The chain $user->getAddress()->getZipCode()->getPostalCode() illustrates this problem.
To simplify, encapsulate the access within methods:
php1class User { 2 private $address; 3 4 public function setAddress(Address $address) { 5 $this->address = $address; 6 } 7 8 public function getUserPostalCode() { 9 return $this->address->getPostalCode(); 10 } 11} 12 13class Address { 14 private $zipCode; 15 16 public function setZipCode(ZipCode $zipCode) { 17 $this->zipCode = $zipCode; 18 } 19 20 public function getPostalCode() { 21 return $this->zipCode->getPostalCode(); 22 } 23} 24 25// Usage 26$user = new User(); 27echo $user->getUserPostalCode();
This adjustment makes the User class responsible for retrieving its postal code, creating a clearer and more direct interface. 📬
A Middle Man problem occurs when a class primarily exists to delegate its functionalities. Here's an example:
php1class Controller { 2 private $service; 3 4 public function __construct(Service $service) { 5 $this->service = $service; 6 } 7 8 public function execute() { 9 $this->service->performAction(); 10 } 11} 12 13class Service { 14 public function performAction() { 15 // Action performed 16 } 17}
The Controller doesn't do much beyond delegating to Service.
To refactor, simplify delegation or reassign responsibilities:
php1class Service { 2 public function performAction() { 3 // Action performed 4 } 5} 6 7// Usage 8$service = new Service(); 9$service->performAction();
By removing the unnecessary middle man, the design becomes more streamlined and efficient. 🔥
In this lesson, you've explored several code smells associated with suboptimal class collaboration and coupling, including Feature Envy, Inappropriate Intimacy, Message Chains, and Middle Man. By identifying and refactoring these smells, you can elevate your code's clarity and maintainability.
Get ready to put these concepts into practice with upcoming exercises, where you'll identify and refactor code smells, strengthening your skills. Keep striving for cleaner, more effective code! 🌟