What is your favorite D feature?

[Seb via Digitalmars-d]

Hi,

I am currently trying to modernize the D code example roulette on 
the dlang.org front page [1]. Hence, I would love to hear about 
your favorite feature(s) in D.
Ideas:
- favorite language construct
- favorite code sample
- "only possible in D"

Before you ask, yes - I want to add a couple of cool examples to 
dlang.org (and yep the roulette rotation is currently broken [2]).

[1] 
https://github.com/dlang/dlang.org/pulls?q=is%3Apr+is%3Aopen+label%3A%22Frontpage+example%22
[2] https://github.com/dlang/dlang.org/pull/1757