Three Cool Things about D

[Steven Schveighoffer via Digitalmars-d-announce]

On 12/22/15 1:29 PM, David Nadlinger wrote:

> ---
> ulong factorial(this n) {
>      return n <= 1 ? 1 : n * factorial(n - 1);
> }
> ---

Am I missing some new feature here? What does the 'this' mean?

-Steve