What are the unused but useful feature you know in D?

[Adam D. Ruppe via Digitalmars-d]

On Monday, 26 June 2017 at 16:51:06 UTC, Moritz Maxeiner wrote:
> As long as you don't introduce immutable by default, resulting 
> in datastructures being littered with `mutable`.

Yeah, I'm against immutable by default. Also, my nogc, safe, etc 
by default idea does NOT apply to main() or virtual methods.

I have explained why before and feel like we are hijacking this 
thread now though....