Upcast A to UndefOr[B1 | B2].
Upcast A to UndefOr[B1 | B2].
This needs evidence that A <: B1 | B2.
(undefOrLowPrioImplicits: StringAdd).self
(undefOrLowPrioImplicits: StringFormat).self
(undefOrLowPrioImplicits: ArrowAssoc[UndefOrLowPrioImplicits]).x
(Since version 2.10.0) Use leftOfArrow instead
(undefOrLowPrioImplicits: Ensuring[UndefOrLowPrioImplicits]).x
(Since version 2.10.0) Use resultOfEnsuring instead