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

[solidstate1991 via Digitalmars-d]

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?

If you need to write a lightweight library or app with no GC and 
Phobos, you can fall back to C functions in core.stdc, my 
wavefile codec/utility (ADPCM, interpolation, resampling, etc.) 
is being written this way.