optionally(_:)
When B
is an Optional
you may call optionally
. The supplied define block creates a subchain which will be run if the Optional value is non-nil. The Link
given to the define block yields a non-optional value of B.WrappedType
to its child links
This function returns a Link
with a void result value, because the subchain defined by optionally will not be executed if B
is nil
.