use v6.d;
unit role MaildirIndexer::Index;
use MaildirIndexer::Email;

method add-mail(MaildirIndexer::Email:D $email, Str:D $mailbox --> Nil) { ... }
method del-path(IO:D $path, Str:D $mailbox --> Nil) { ... }
method mailbox-for-email(MaildirIndexer::Email:D $email --> Str) { ... }