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

[Moritz Maxeiner via Digitalmars-d]

On Monday, 26 June 2017 at 16:10:01 UTC, H. S. Teoh wrote:
> On Mon, Jun 26, 2017 at 02:39:30PM +0000, Mike Parker via 
> Digitalmars-d wrote:
>> On Monday, 26 June 2017 at 14:17:26 UTC, Adam D. Ruppe wrote:
>> 
>> > 
>> > So here's how I'd do it:
>> > 
>> > 1) Add the opposite attributes: `impure`, `throws`, `@gc`, 
>> > etc. 2) Add the module version thing that changes defaults 
>> > on request 3) imagine more potential going forward
>> > 
>> > 
>> > It isn't even hard.
>> 
>> And along with that a compiler switch to enable strict mode by 
>> default.
>> 
>> If you, or anyone else, is willing to put this in DIP form, 
>> I'll gladly do what I can to help minimize the effort required 
>> to write it up. This is something I'd love to see.
>
> 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`.