PHP SOLID Principles
SOLID is an acronym for the first five object-oriented design principles by Robert C. Martin. These principles help make software designs more understandable, flexible, and maintainable.
1. Single Responsibility Principle (SRP)
A class should have only one reason to change. It should have only one job.
// Bad: Handles user data AND email logic
class User {
public function save() { /* ... */ }
public function sendEmail() { /* ... */ }
}
// Good: Separate responsibilities
class User {
public function save() { /* ... */ }
}
class EmailService {
public function send(User $user) { /* ... */ }
}2. Open/Closed Principle (OCP)
Software entities should be open for extension, but closed for modification.
interface Shape {
public function area();
}
class Rectangle implements Shape {
public function area() { /* ... */ }
}
class Circle implements Shape {
public function area() { /* ... */ }
}
// We can add new shapes without modifying the AreaCalculator
class AreaCalculator {
public function calculate(array $shapes) {
$area = 0;
foreach ($shapes as $shape) {
$area += $shape->area();
}
return $area;
}
}3. Liskov Substitution Principle (LSP)
Objects of a superclass shall be replaceable with objects of its subclasses without breaking the application.
If Bird is the parent and Penguin is the child, Penguin should not break code expecting a Bird. If Bird has a fly() method, Penguin shouldn't throw an exception when fly() is called.
4. Interface Segregation Principle (ISP)
Clients should not be forced to depend upon interfaces that they do not use. Split large interfaces into smaller ones.
// Bad
interface Worker {
public function work();
public function eat();
}
// Good
interface Workable {
public function work();
}
interface Feedable {
public function eat();
}5. Dependency Inversion Principle (DIP)
High-level modules should not depend on low-level modules. Both should depend on abstractions.
interface DBConnectionInterface {
public function connect();
}
class PasswordReminder {
private $db;
public function __construct(DBConnectionInterface $db) {
$this->db = $db;
}
}programming/php/php programming/php/php-classes programming/php/php-design-patterns