RACSignal map with error - ios

Question

I have a simple question but I can't find a nice solution to it.
I have a signal that sends strings, and a map after it. The map converts the strings into JSON.
It may happen that the string has a wrong format and the JSON parser will fail to parse with an error.
[stringGeneratorSignal map:^(NSString *bussinessObjectString){
NSError *error;
BussinessObject *obj = [[BussinessObject alloc] initWithString:bussinessObjectString error:&error];
if (error) {
NSLog(#"%#", error);
}
return obj;
}];
But because I'm inside the map I can't return an error signal. What I would like is to get an error with the error provided by the parser.
A couple of possibilities I've analyzed that I don't like:
Return the error in the map and then have a wrapper signal that actually convert the data (or error) into an error signal. The problem is that I'm delegating the same problem (converting the data into an error signal).
Use flattenMap instead. This will allow to return an error message, but the problem is that it's not the same behaviour as map.
What is the best approach for this kind of scenarios?
Thanks!

Answer 1

Look at -tryMap. It allows you to return data or nil and then set the error
/// Runs `mapBlock` against each of the receiver's values, mapping values until
/// `mapBlock` returns nil, or the receiver completes.
///
/// mapBlock - An action to map each of the receiver's values. The block should
/// return a non-nil value to indicate that the action was successful.
/// This block must not be nil.
///
/// Example:
///
/// // The returned signal will send an error if data cannot be read from
/// // `fileURL`.
/// [signal tryMap:^(NSURL *fileURL, NSError **errorPtr) {
/// return [NSData dataWithContentsOfURL:fileURL options:0 error:errorPtr];
/// }];
///
/// Returns a signal which transforms all the values of the receiver. If
/// `mapBlock` returns nil for any value, the returned signal will error using
/// the `NSError` passed out from the block.
- (RACSignal *)tryMap:(id (^)(id value, NSError **errorPtr))mapBlock;