PHP依赖注入实现方法详解

class DatabaseConnection {
    public function query($sql) {
        // 模拟查询
        return "result from $sql";
    }
}
class UserService {
private $db;
// 通过构造函数注入依赖
public function __construct(DatabaseConnection $db) {
    $this->db = $db;
}

public function getUser($id) {
    return $this->db->query("SELECT * FROM users WHERE id = $id");
}
}
// 使用时由外部创建并传入
$db = new DatabaseConnection();
$userService = new UserService($db);
echo $userService->getUser(1);

class Container {
    private $definitions = [];
    private $instances = [];
// 绑定接口或类到具体实现
public function bind($abstract, $concrete = null) {
    if ($concrete === null) {
        $concrete = $abstract;
    }
    $this->definitions[$abstract] = $concrete;
}

// 获取实例
public function get($abstract) {
    if (isset($this->instances[$abstract])) {
        return $this->instances[$abstract];
    }

    $concrete = $this->definitions[$abstract] ?? $abstract;

    // 如果是可调用的，执行它
    if (is_callable($concrete)) {
        $object = $concrete($this);
    } else {
        $object = $this->build($concrete);
    }

    $this->instances[$abstract] = $object;
    return $object;
}

// 根据类的构造函数自动解析依赖
public function build($className) {
    $reflector = new ReflectionClass($className);

    if (!$reflector->isInstantiable()) {
        throw new Exception("Can't instantiate $className");
    }

    $constructor = $reflector->getConstructor();

    if (!$constructor) {
        return new $className;
    }

    $parameters = $constructor->getParameters();
    $dependencies = [];

    foreach ($parameters as $param) {
        $type = $param->getType();
        if ($type && !$type->isBuiltin()) {
            $dependencies[] = $this->get($type->getName());
        } else {
            if (!$param->isDefaultValueAvailable()) {
                throw new Exception("Cannot resolve parameter: {$param->getName()}");
            }
            $dependencies[] = $param->getDefaultValue();
        }
    }

    return $reflector->newInstanceArgs($dependencies);
}
}

class Logger {
    public function log($message) {
        echo "[LOG] $message\n";
    }
}
class Mailer {
private $logger;
public function __construct(Logger $logger) {
    $this->logger = $logger;
}

public function send($to, $msg) {
    $this->logger->log("Email sent to $to: $msg");
}
}
class UserRegistration {
private $mailer;
private $logger;
public function __construct(Mailer $mailer, Logger $logger) {
    $this->mailer = $mailer;
    $this->logger = $logger;
}

public function register($email) {
    $this->logger->log("Registering user: $email");
    $this->mailer->send($email, "Welcome!");
}
}

$container = new Container();
// 注册服务
$container->bind(Logger::class);
$container->bind(Mailer::class);
$container->bind(UserRegistration::class);
// 获取实例（自动注入所有依赖）
$registration = $container->get(UserRegistration::class);
$registration->register('user@example.com');

[LOG] Registering user: user@example.com
[LOG] Email sent to user@example.com: Welcome!