How would you solve this 'interview' question in D?

[Adam D. Ruppe]

On Wednesday, 26 June 2013 at 20:51:35 UTC, Gary Willoughby wrote:
> Just for a bit of fun, I saw this question posted on reddit the 
> other day and wondered how *you* would solve this in D?

Since they didn't say *pure* function, I'd cheat:

int f(int n) {
   static bool isOddCall;
   isOddCall = !isOddCall;
   if(!isOddCall)
       return -n;
   return n;
}

:P