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

[Jon Degenhardt]

On Tuesday, 7 November 2017 at 17:15:02 UTC, Gary Willoughby 
wrote:
> On Sunday, 25 June 2017 at 23:21:25 UTC, aberba wrote:
>> Can you share feature(s) in D people are not talking about 
>> which you've found very useful?
>
> Some of the best features are in the standard library. I've 
> written about them here:
>
> http://nomad.so/2014/08/hidden-treasure-in-the-d-standard-library/
> http://nomad.so/2015/08/more-hidden-treasure-in-the-d-standard-library/

It's mentioned in Gary's articles, but std.conv.to is fantastic.