Challenge: Make a data type for holding one of 8 directions allowing increment and overflow

[Daniel N]

On Tuesday, 12 March 2024 at 05:38:03 UTC, Liam McGillivray wrote:
> I am in need of a data type for holding direction information; 
> one of 8 directions on a single axis. They are named in terms 
> of compass directions. If D had a 4-bit datatype, I would just 
> use this and do `+=2` whenever I want to change the datatype, 
> but it doesn't.
>
> Perhaps this would be a good programming challenge for someone 
> more experienced than me. Make a data type (probably a struct) 
> for holding one of 8 directional values using 3 bits. It should 
> accept the use of increment operators to change the angle.
>
> Ideally (but optionally), it should work as an enum of the same 
> name; "Direction".
>
> Here's a unittest that it should ideally pass:

D actually supports both 3 and 4 bit integers. People will likely 
warn you of minor portability risks... but if you target a 
limited amount of platforms and prefer concise readable code, 
then it's a text book example for bitfields. The risk can easily 
be mitigated by having an unittest to catch the error directly(if 
you try to port to some exotic platform).

dmd -preview=bitfields

(Some lines stolen from Rikki)

```d
struct Direction
{
     private uint value : 3;
     alias this = value;

     enum Direction N  = Direction(0);
     enum Direction NE = Direction(1);
     enum Direction E  = Direction(2);
     enum Direction SE = Direction(3);
     enum Direction S  = Direction(4);
     enum Direction SW = Direction(5);
     enum Direction W  = Direction(6);
     enum Direction NW = Direction(7);
}
```