これは非常に面倒です
RACSignal *originalSignal = ...;
RACSignal *mappedSignal = [[[[[originalSignal publish] autoconnect] materialize] map:^id(RACEvent *event) {
if(event.eventType == RACEventTypeError)
{
return [RACEvent eventWithError:[self errorForHelperError:event.error]];
}
return event;
}] dematerialize];