What is the concept of Dependency Injection in PHP and how can it be applied to improve code structure?

Dependency Injection is a design pattern in which the dependencies of a class are injected from the outside rather than created within the class itself. This helps improve code structure by promoting loose coupling, making classes easier to test, reuse, and maintain. 

// Example of Dependency Injection in PHP

class Database {
    private $connection;

    public function __construct($host, $username, $password, $database) {
        $this->connection = new PDO("mysql:host=$host;dbname=$database", $username, $password);
    }

    public function query($sql) {
        return $this->connection->query($sql);
    }
}

class UserRepository {
    private $database;

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

    public function getUsers() {
        $result = $this->database->query("SELECT * FROM users");
        return $result->fetchAll();
    }
}

// Usage
$database = new Database('localhost', 'root', 'password', 'mydatabase');
$userRepository = new UserRepository($database);
$users = $userRepository->getUsers();

Keywords

Dependency Injection PHP code structure design pattern object-oriented programming

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