This member is added by an implicit conversion from UnboundedMailbox to
any2stringadd[UnboundedMailbox] performed by method any2stringadd in scala.Predef.
This member is added by an implicit conversion from UnboundedMailbox to
StringFormat[UnboundedMailbox] performed by method StringFormat in scala.Predef.
UnboundedMailbox is the default unbounded MailboxType used by Akka Actors.