code: public function getInstance(\ReflectionClass $impl, InjectionProvider $provider)
      {
          $key = $impl->getName();
          if (!isset($this->instances[$key])) {
              $this->instances[$key] = $provider->get();
          }
  
          return $this->instances[$key];
      }
docs: returns the requested instance from the scope
  
  @param   \ReflectionClass                 $impl      concrete implementation
  @param   \stubbles\ioc\InjectionProvider  $provider
  @return  object