public static function genericKeys() : array
    {
        if (static::$externalContainer) {
            $container = static::$externalContainer;
            // Pimple.
            if (method_exists($container, 'keys')) {
                return $container->keys();
            }
            // PHP-DI.
            if (method_exists($container, 'getKnownEntryNames')) {
                return $container->getKnownEntryNames();
            }
            // ArrayObject
            if (method_exists($container, 'getArrayCopy')) {
                return array_keys($container->getArrayCopy());
            }
            throw new ContainerLogicException(
                'Externale container type[' . get_class($container) . '] provides no known means of accessing'
            );
        }
        if (static::$internalContainer) {
            return array_keys(static::$internalContainer->keys);
        }
        return [];
    }