PHP design patterns: relationship to design principles

PHP Design Patterns: Relationship to Design Principles

Introduction

Design patterns are software Developing reusable solutions to common problems. They are based on design principles such as SOLID (single responsibility, open-closed, dependency inversion, interface isolation, Liskov substitution). Understanding design principles is crucial to effectively applying design patterns in PHP.

Design Principles

Single Responsibility Principle (SRP): Each class or module should be responsible for only one function. This enhances maintainability and testability.

Open-Closed Principle (OCP): Software should be easy to extend, but difficult to modify. This means that interfaces and abstract classes should be used instead of concrete classes.

Dependency Inversion Principle (DIP): High-level modules should not depend on low-level modules. Instead, they should rely on abstract interfaces or base classes.

Interface Segregation Principle (ISP): An interface should be as narrow as possible, containing only required methods. This reduces coupling and improves scalability.

Liskov Substitution Principle (LSP): A subclass should be able to seamlessly replace its parent class. This means that subclasses must abide by the contract of the parent class.

Design Pattern

Factory Method Pattern: It provides an interface for creating objects without specifying the concrete class of the object. This allows different classes of objects to be created in different situations.

Practical Case

interface ShapeFactory {
    public function createShape(string $type);
}

class CircleFactory implements ShapeFactory {
    public function createShape(string $type): Shape {
        return new Circle();
    }
}

class RectangleFactory implements ShapeFactory {
    public function createShape(string $type): Shape {
        return new Rectangle();
    }
}

class Shape {
    public function draw() {
        echo "Drawing a shape.\n";
    }
}

class Circle extends Shape {
    public function draw() {
        echo "Drawing a circle.\n";
    }
}

class Rectangle extends Shape {
    public function draw() {
        echo "Drawing a rectangle.\n";
    }
}

$factory = new CircleFactory();
$shape = $factory->createShape("circle");
$shape->draw();

This example demonstrates the factory method pattern, which creates a specific shape object based on the type. It follows OCP in that we can add new shape types without modifying the Shape class. It also follows DIP because Factory relies on the ShapeFactory interface rather than a concrete Shape class.

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