code: public function resolve(string $variable)
      {
          $matches = [];
  
          if (!$this->isMatch($variable, $matches)) {
              throw new UnresolvedException('Variable pattern "'.$variable.'" is not valid.');
          }
  
          $service = $matches[1];
          $resource = $matches[2];
          $id = $matches[3];
          $property = $matches[4];
          $model = $this->api->get($service.'.'.$resource)->get($id);
          $accessor = PropertyAccess::createPropertyAccessor();
  
          try {
              $value = $accessor->getValue($model, $property);
          } catch (Exception $exception) {
              throw new UnresolvedException('Variable pattern "'.$variable.'" is not valid.', 0, $exception);
          }
  
          return $value;
      }
docs: {@inheritdoc}