Dependency Inversion Principle in PHP

Question

Since PHP is a loosely typed language, how can the DIP principle be applied in PHP?

A practical example would be greatly appreciated.

Answer 1

PHP 5 introduced "Type Hinting", which enables functions and methods to declare "typed" parameters (objects). For most cases, it should be not a big task to port examples, e.g. from Java, to PHP 5.

A really simple example:

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()
  {
    // ...
  }
}