RAC_Cache.m

//the trick is to use replayLast or replayLazily signal operation, which basically creates buffer and hold in it cached value! 

- (void)getData:(id)inputParam forKey:(NSString *)key withCompletionBlock:(void (^)(id data, NSError *error)) {
    if (!_cache[key]) {
        RACSignal *dataSignal = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
            id operation = _actualGetDataRequest(inputParam, ^(id data, NSError *error) {
                if (error) {
                    [subscriber sendError:error];
                }
                else {
                    [subscriber sendNext:asyncActionResult];
                    [subscriber sendCompleted];
                }
            });
            return [RACDisposable disposableWithBlock:^{
                [operation cancel];
            }];
        }];
        _cache[key] = dataSignal.replayLast;
    }
    if (completionBlock) {
        RACSignal *cachedSignal = _cache[key];
        [cachedSignal subscribeNext:^(id data){
            completionBlock:(data, nil);
        } error: ^(NSError *error) {
            completioBlock:(nil, error);
            }]
    }   

}