在PHP中，依賴注入（Dependency Injection，簡稱DI）是一種設計模式，用于降低代碼之間的耦合度。通過使用反射，我們可以在運行時動態地實例化和注入依賴。以下是一個簡單的示例，展示了如何使用PHP反射實現依賴注入：

1. 首先，創建一個接口和兩個實現類：

interface MyInterface
{
    public function doSomething();
}

class MyImplementationA implements MyInterface
{
    public function doSomething()
    {
        echo "MyImplementationA doSomething\n";
    }
}

class MyImplementationB implements MyInterface
{
    public function doSomething()
    {
        echo "MyImplementationB doSomething\n";
    }
}

2. 創建一個容器類，用于處理依賴注入：

class Container
{
    private $instances = [];

    public function set($key, $instance)
    {
        if (!is_object($instance)) {
            throw new InvalidArgumentException('Instance must be an object');
        }
        $this->instances[$key] = $instance;
    }

    public function get($key)
    {
        if (!isset($this->instances[$key])) {
            throw new InvalidArgumentException('No instance found for key: ' . $key);
        }
        return $this->instances[$key];
    }
}

3. 使用反射實現依賴注入：

function resolveDependencies(Container $container, array $typeHints)
{
    $reflection = new ReflectionClass($typeHints['class']);
    $constructor = $reflection->getConstructor();

    if ($constructor === null) {
        throw new InvalidArgumentException('Class ' . $typeHints['class'] . ' has no constructor');
    }

    $dependencies = [];
    foreach ($constructor->getParameters() as $parameter) {
        $dependencyName = $parameter->getName();
        if (!isset($container->get($dependencyName))) {
            throw new InvalidArgumentException('Dependency ' . $dependencyName . ' not found');
        }
        $dependencies[] = $container->get($dependencyName);
    }

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

4. 使用依賴注入容器：

$container = new Container();

$container->set('myInterface', resolveDependencies($container, [
    'class' => MyInterface::class,
    'dependencies' => [MyImplementationA::class, MyImplementationB::class],
]));

$instance = $container->get('myInterface');
$instance->doSomething(); // Output: MyImplementationA doSomething

在這個示例中，我們創建了一個簡單的依賴注入容器，它使用反射來動態地實例化和注入依賴。resolveDependencies函數接受一個容器實例和一個類型提示數組，然后使用反射來獲取類的構造函數和依賴項。接下來，它從容器中獲取這些依賴項并使用它們來實例化類。最后，我們使用這個容器來實例化一個實現了MyInterface接口的類，并調用其doSomething方法。