How can Dependency Injection be used to add instances to a class in PHP?

Dependency Injection is a design pattern used to inject dependencies into a class instead of the class creating its dependencies internally. This promotes loose coupling and makes the code more testable and maintainable. In PHP, you can achieve Dependency Injection by passing instances of dependencies to a class through its constructor or setter methods. 

// Example of using Dependency Injection in PHP

class Database {
    public function query($sql) {
        // Database query logic
        return "Query executed: $sql";
    }
}

class UserRepository {
    private $db;

    public function __construct(Database $db) {
        $this->db = $db;
    }

    public function getUserById($id) {
        $sql = "SELECT * FROM users WHERE id = $id";
        return $this->db->query($sql);
    }
}

// Usage
$db = new Database();
$userRepository = new UserRepository($db);
echo $userRepository->getUserById(1);

Keywords

Dependency Injection class instances PHP object-oriented programming constructor injection

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