Implement a Substring Closure within a Range in Objective C

substring.m

  // Substring Closure
  // Similar for what found in other languages  
  // Usage 
  // substring(@"my-string", 2, 4);
  // => -st
  
  NSString * ( ^ substring ) (NSString *, int , int);
  
  substring = ^(NSString * string, int from, int to) {
    
    NSString * digit = @"";
    NSMutableString * sub = [@"" mutableCopy];
    
    for (int i = from; i < to; i++) {
      digit = [NSString stringWithFormat:@"%c", [string characterAtIndex:i]];
      [sub appendString:digit];
    }
    
    NSLog(@"Substring %@ From %d To %d Result %@ ", string, from, to, sub);
    
    return sub;
  };