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

[Moritz Maxeiner via Digitalmars-d]

On Monday, 26 June 2017 at 16:51:06 UTC, Moritz Maxeiner wrote:
> On Monday, 26 June 2017 at 16:10:01 UTC, H. S. Teoh wrote:
>>
>> Yes, please do!  If we can push this through, D could be in a 
>> much, much better place in a few years' time!
>
> As long as you don't introduce immutable by default, resulting 
> in datastructures being littered with `mutable`.

Addendum: I'm also not in favor of `nothrow` by default, because 
imho that contradicts D's error handling using exceptions by 
default.