Verschiedene Implementierungen einer Client-Klasse mit einer optionalen Abhängigkeit.

gistfile1.php

<?php

/**
* Something the Client may depend on or not.
*/
interface Dependency{
	public function action();}

/**
* The Client.
*/
interface Client{
	public function doSomething();}

/**
* Implementation of the dependency which will do something.
*/
class UsefulDependencyImplementation implements Dependency{
	public function action(){
		/* Do something. */}}

/**
* Client implementation using setter injection. The dependency may or may not
* be injected.
*/
class ClientImplementationWithOptionalDependency implements Client{
	private $dep;

	public function setDependency(Dependency $dep){
		$this->dep = $dep;}

	public function doSomething(){
		/* Some client logic. */
		if (isset($this->dep)){
			$this->dep->action();}
		/* Some client logic. */}}

/**
* Null implementation of the dependency. Does nothing.
*/
class DependencyNullImplementation implements Dependency{
	public function action(){}}

/**
* Client implementation which needs always an object satisfying the
* Dependency's interface.
*/
class ClientImplementationWithMandatoryDependency implements Client{
	private $dep;

	public function __construct(Dependency $dep){
		$this->dep = $dep;}

	public function doSomething(){
		/* Some client logic. */
		$this->dep->action();
		/* Some client logic. */}}

// Create client using the dependency.
$client = new ClientImplementationWithOptionalDependency();
$client->setDependency(new UsefulDependencyImplementation());

// Create client not using the dependency.
$client = new ClientImplementationWithOptionalDependency();

// Create client using the dependency.
$client = new ClientImplementationWithMandatoryDependency(new UsefulDependencyImplementation());

// Create client not using the dependency.
$client = new ClientImplementationWithMandatoryDependency(new DependencyNullImplementation());