block in ios: what is this method map: before a block? - ios

Question

I don't understand what map: is, in the tutorial using blocks, I could not find a map method in RACSignal (link) or RACDisposable (link) .
- (RACSignal *)fetchJSONFromURL:(NSURL *)url {
NSLog(#"Fetching: %#",url.absoluteString);
// 1
return [[RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
// 2
NSURLSessionDataTask *dataTask = [self.session dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
// TODO: Handle retrieved data
}];
// 3
[dataTask resume];
// 4
return [RACDisposable disposableWithBlock:^{
[dataTask cancel];
}];
}] doError:^(NSError *error) {
// 5
NSLog(#"%#",error);
}];
}
- (RACSignal *)fetchCurrentConditionsForLocation:(CLLocationCoordinate2D)coordinate {
// 1
NSString *urlString = [NSString stringWithFormat:#"http://api.openweathermap.org/data/2.5/weather?lat=%f&lon=%f&units=imperial",coordinate.latitude, coordinate.longitude];
NSURL *url = [NSURL URLWithString:urlString];
// 2
return [[self fetchJSONFromURL:url] map:^(NSDictionary *json) {
// 3
return [MTLJSONAdapter modelOfClass:[WXCondition class] fromJSONDictionary:json error:nil];
}];
}
The link of the tutorial from raywenderlich website : link
Thanks
//...'map' callback
- (RACSignal *)fetchCurrentConditionsForLocation:(CLLocationCoordinate2D)coordinate {
// 1
NSString *urlString = [NSString stringWithFormat:#"http://api.openweathermap.org/data/2.5/weather?lat=%f&lon=%f&units=imperial",coordinate.latitude, coordinate.longitude];
NSURL *url = [NSURL URLWithString:urlString];
// 2
return [[self fetchJSONFromURL:url] map:^(NSDictionary *json) {
// 3
return [MTLJSONAdapter modelOfClass:[WXCondition class] fromJSONDictionary:json error:nil];
}];
}
//... 'map' method
- (instancetype)map:(id (^)(id value))block {
NSCParameterAssert(block != nil);
Class class = self.class;
return [[self flattenMap:^(id value) {
return [class return:block(value)];
}] setNameWithFormat:#"[%#] -map:", self.name];
}

Answer 1

apply the block to every item in the given array and then return the results of each mapping

Answer 2

It's defined in RACSignal's superclass, RACStream:
/// Maps `block` across the values in the receiver.
///
/// This corresponds to the `Select` method in Rx.
///
/// Returns a new stream with the mapped values.
- (instancetype)map:(id (^)(id value))block;