If PHP Were British (2011)(aloneonahill.com)

  interface CacheStrategyInterface {
    public function shouldCache(Request $request, Response $response): bool;
  }

  class DefaultStrategy implements CacheStrategyInterface {
    public function shouldCache(Request $request, Response $response): bool {
      if ( ! $this->isMethodCachable($request)) {
        return false;
      }

      return $this->isSuccessful($response);
    }

    // This method can be modified by user code: Maybe they implemented 
    // an API with a `"success": false` in the response body, despite 
    // the status code? There's no way to know that, let alone provide a
    // configuration switch for every possible failure condition in user
    // code implementing our middleware.
    protected function isSuccessful(Response $response): bool {
      return $response->isSuccessful() || $response->isRedirection();
    }

    // This method shall not be modified: Whether an HTTP request may be
    // cached is defined by specification, not implementation.
    private function isMethodCachable(Request $request): bool {
      return $request->isMethodCacheable();
    }
  }

  class CustomStrategy extends DefaultStrategy {
    protected function isSuccessful(Response $response): bool {
      return $response->body('success', false) === true;
    }
  }

  Falls etwas     nicht gleich   null ist.
  if    something not   ==       null

  Falls etwas     nicht ungleich null ist.
  if    something not   !=       null

    falls etwas nichtet

  $x = foo() unless $y > 10