In Drupal 7 I use devel's drupal_debug() or its alias dd() to log a variable to a drupal_debug.txt in the site's temp directory.
In the Drupal 8 version of devel this function has disappeared. It seems to be replaced by DevelDumperManagerInterface But it is not clear to me how it used.
How can I log variables to a txt file in Drupal 8?
drupal_set_message(var_dump($variable), 'warning');