Completing C code with D style

[kdevel]

On Thursday, 4 November 2021 at 00:53:11 UTC, jfondren wrote:
> On Wednesday, 3 November 2021 at 20:36:08 UTC, russhy wrote:
>> Keeping things simple helps debugging!
>
> I'd still have to run your program to be sure of its simple 
> logic, though. The real star d feature that would help with 
> debugging is unittest:

What about the number 0 (zero)? If 0 is considered to be excluded 
from the domain how would one define in D a type which cannot 
represent 0 in the first place? Follow-up question: Are there 
language facilities such that one could initialize an array of 
these non-zero-ints like?:

```
    nzint [] numbers = [ -2, -1, 1, 2 ];
```

If 0 is included in the domain the classification of the values 
into negative and positive ones is not complete since 0 is 
neither.

```
enum sign { negatives = 'n', positives = 'p', both = 'b' }
enum parity { evens = 'e', odds = 'o', both = 'b' }

bool simple(int n, sign s, parity p) {
     if (n < 0 && s == sign.positives) return false;
     if (n > 0 && s == sign.negatives) return false;
     if (n & 1) {
         if (p == parity.evens) return false;
     } else {
         if (p == parity.odds) return false;
     }
     return true;
}

unittest {
     import std.algorithm : filter, equal;
     version (have_zero) {
         auto numbers = [-2, -1, 0, 1, 2];
     }
     else {
         auto numbers = [-2, -1, 1, 2];
     }
     alias match = (ns, s, p) => ns.equal(numbers.filter!(n => 
simple(n, s, p)));

     assert(match(numbers, sign.both, parity.both));
     assert(match([-1], sign.negatives, parity.odds));
     assert(match([-2], sign.negatives, parity.evens)); // fails 
when we have_zero
     assert(match([2], sign.positives, parity.evens));
     assert(match([1], sign.positives, parity.odds));
     assert(match([-2, -1], sign.negatives, parity.both));
     assert(match([-2, 2], sign.both, parity.evens));
}
```

```shell
$ dmd -version=have_zero -checkaction=context -unittest -main 
-run a.d
a.d(27): [unittest] false != true
1/1 modules FAILED unittests

```