sequence

sequence.m

typedef void (^OpCompletionEither)(BOOL success);

- (void)sequence:(NSArray *)selectors
  withFinalBlock:(OpCompletionEither)block {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
  __block OpCompletionEither _block = block;
  SEL selector = NSSelectorFromString(selectors[0]);
  if (selectors.count == 1)
    // last request, perform reply block
    [self performSelector:selector withObject:_block];
  else
    [self performSelector:selector withObject:^(BOOL success) {
      // iterate on tail
      NSRange tailRange = {1, selectors.count - 1};
      [self  sequence:[selectors subarrayWithRange:tailRange]
       withFinalBlock:_block];
    }];
#pragma clang diagnostic pop
}


/* usage */

[self  sequence:@[NSStringFromSelector(@selector(getCitiesWithBlock:)),
                 NSStringFromSelector(@selector(getSubwaysWithBlock:))]
 withFinalBlock:^(BOOL success) {
    NSLog(@"%@", success ? @"ok" : @"fail");
}];