PHP中的依赖倒置原则

interface MyClient
{
  public function doSomething();
  public function doSomethingElse();
}

class MyHighLevelObject
{
  private $client;

  public __construct(MyClient $client)
  {
    $this->client = $client;
  }

  public function getStuffDone()
  {
    if ( any_self_state_check_or_whatever )
      $client->doSomething();
    else
      $client->doSomethingElse();
  }

  // ...
}

class MyDIP implements MyClient
{
  public function doSomething()
  {
    // ...
  }

  public function doSomethingElse()
  {
    // ...
  }
}