Can wp_list_comments output into variable?

Question

In the default usage this is impossible due to the nature of the default comment walker which always directly outputs. But the function allows to provide a custom walker.

Further reading about custom walkers:
Codex Class reference
example custom walker class

You could also use output buffering to save it into a variable (this is considered to be dirty):

ob_start();
wp_list_comments(array('reverse_top_level' => false ), $comments);
$variable = ob_get_clean();