gistfile1.txt

<?php

interface WebserviceInterface
{
  public function getFoo();
}

class Webservice implements WebserviceInterface
{
  public function getFoo()
  {
    return 'bar';
  }
}

class WebserviceImplementation
{
  public function __construct(WebserviceInterface $webservice)
  {
    $this->webservice = $webservice;
  }

  public function doSomethingWithFoo()
  {
    $this->webservice->getFoo();
  }
}