Handling errors when using toProperty:onObject:.

gistfile1.m

RAC(self.someOrderedSet) = [[[[[[RACAble(self.searchField.text)      
  filter:^BOOL(NSString *text) {
    return (text.length > 0);
  }]
  map:^id(NSString *text) {
    return [Something searchForAutocomplete:text]; // this signal can send errors
  }]
  switchToLatest]
  catchTo:[RACSignal return:[NSArray array]]]
  map:^id(NSArray *objects) {
    NSMutableOrderedSet *orderedSet = [NSMutableOrderedSet orderedSet];
    [orderedSet addObjectsFromArray:objects];
    return orderedSet;
  }]
  retry];

It's much more likely you want to catch errors directly from +searchForAutocomplete: instead of on the switched signal. That way you don't need to worry about that signal ending with an error:

[[[[RACAble(self.searchField.text)      
  filter:^BOOL(NSString *text) {
    return (text.length > 0);
  }]
  map:^id(NSString *text) {
    return [[Something searchForAutocomplete:text] catchTo:[RACSignal return:@[]]];
  }]
  switchToLatest]
  map:^id(NSArray *tickers) {
    NSMutableOrderedSet *orderedSet = [NSMutableOrderedSet orderedSet];
    [orderedSet addObjectsFromArray:tickers];
    return orderedSet;
  }];