Metaprog can be abstruse

[kdevel]

On Monday, 4 July 2022 at 09:40:45 UTC, Bastiaan Veelo wrote:
> [...]
> Not necessarily.
> ```d
> immutable decimalRanks = iota(10).map!(p => 10.pow(p)).array;
> ```

Your example requires

```
import std.range; // for iota
import std.algorithm; // for map
import std.math; // for pow of int
```

Then your example is prone to errors:

```
immutable decimalRanks = iota(13).map!(p => 10.pow(p)).array; // 
silent wrap around
```

(unit)test to the rescue:

```
auto make_decimal_rank ()
{
    import std.range;
    import std.algorithm;
    import std.math;
    return iota (13).map!(p => 10.pow (p)).array;
}

void main ()
{
    import std.stdio;
    immutable decimalRank = make_decimal_rank;
    decimalRank.writeln;
    typeof (decimalRank).stringof.writeln;
}

unittest {
    enum ar13 = [
          1,
          10,
          100,
          1000,
          10000,
          100000,
          1000000,
          10000000,
          100000000,
          1000000000,
          10000000000,
          100000000000,
          1000000000000
       ];
    pragma (msg, typeof (ar13));
    assert (make_decimal_rank == ar13);
}
```

Running:

```
dmd -checkaction=context -unittest -run decrank
long[]
decrank.d(35): [unittest] [1, 10, 100, 1000, 10000, 100000, 
1000000, 10000000, 100000000, 1000000000, 1410065408, 1215752192, 
-727379968] != [1, 10, 100, 1000, 10000, 100000, 1000000, 
10000000, 100000000, 1000000000, 10000000000, 100000000000, 
1000000000000]
1/1 modules FAILED unittests
```