That ## vals syntax is new to me. What's the difference with the following?

  #define MD(...) [NSMutableDictionary dictionaryWithObjectsAndKeys:__VA_ARGS__, nil]

Both of them wouldn't work for MD() due to the trailing nil.

But for MD(val, key, vals...), it'd give you a slightly better error, complaining about the number of arguments when you do MD().

Otherwise they are the same in this case.

## removes one non-whitespace character – often the comma – before the ## if vals or __VA_ARGS__ is empty.

e.g

  #define MO_LogDebug(fmt, ...) NSLog((@"DEBUG " fmt), ##__VA_ARGS__)

  MO_LogDebug(@"This works as expected %d", resultCode);

  // Removes the comma automatically in here:
  // NSLog((@"DEBUG " @"This works too without args"), );
  MO_LogDebug(@"This works too without args");

Very nice, thanks for that.