Single Responsibility Principle (SRP)

1. Introduction

The Single Responsibility Principle is one of the five SOLID principles of object-oriented design. It states that a class should have only one reason to change, meaning it should have only one job or responsibility.

2. Definition

Single Responsibility Principle (SRP): A class should have one and only one reason to change. This means that a class should only have one responsibility or job.

3. Importance

• Enhances code readability and maintainability.
• Reduces the impact of changes.
• Improves testability of the code.
• Facilitates better separation of concerns.

4. Code Examples

4.1 Bad Example

class User {
    public function createUser($data) {
        // Logic to create user
    }
    
    public function sendEmail($email) {
        // Logic to send email
    }
    
    public function logUserActivity($activity) {
        // Logic to log user activity
    }
}

In this example, the User class has multiple responsibilities: creating a user, sending an email, and logging activity.

4.2 Good Example

class User {
    public function createUser($data) {
        // Logic to create user
    }
}

class EmailService {
    public function sendEmail($email) {
        // Logic to send email
    }
}

class ActivityLogger {
    public function logUserActivity($activity) {
        // Logic to log user activity
    }
}

Here, each class has a single responsibility. The User class only handles user creation, EmailService handles email, and ActivityLogger manages logging.

5. Best Practices

• Identify responsibilities in your classes and separate them.
• Refactor classes that have multiple reasons to change.
• Use interfaces to define single responsibilities.
• Consider using dependency injection to manage dependencies effectively.

6. FAQ