Re: How to obtain Variant underlying type?

[jfondren via Digitalmars-d-learn]

On Monday, 11 July 2022 at 03:17:33 UTC, anonymouse wrote:
On Sunday, 10 July 2022 at 18:31:46 UTC, drug007 wrote:

I'd like to say that using of exception to break loop is 
really bad. Exception is exceptional thing but in the case 
above the exception is ordinary completion of the loop happens 
on regular basis. Don't do that.

Thanks for the advice. Lesson learned.

--anonymouse

Oh, sorry. I didn't defend the code in any way because I assumed 
that the exceptional design would be seen as obviously bad (and 
that someone else would dig harder in order to find a better 
solution).

The TypeInfo_Array fix breaks the last assertion of those unit 
tests, though. This works:

```d
import std.variant : Variant;

size_t[] shape(Variant v) {
    size_t[] s;
    while (cast(TypeInfo_Array) v.type !is null && v.length > 0) {
        Variant elem = v[0];
        s ~= v.length;
        v = elem;
    }
    return s;
}
```

Although, that last assertion really is debatable. Languages like 
APL would read it as having a shape of [2, 0]:

```d
import std.variant : Variant;

size_t[] shape(Variant v) {
    size_t[] s;
    while (cast(TypeInfo_Array) v.type !is null) {
        s ~= v.length;
        if (!v.length) break;
        v = v[0];
    }
    return s;
}

unittest {
    assert([3, 1] == [[1], [2], [3]].Variant.shape);
    assert([2, 1] == [[1], [2]].Variant.shape);
    assert([2, 2] == [[1, 0], [2, 0]].Variant.shape);
    assert([2] == [1, 2].Variant.shape);
    assert([] == 2.Variant.shape);
    assert([2, 0] == [[], []].Variant.shape);

    // irregularity not checked
    assert([2, 2] == [[1, 0], [2]].Variant.shape);
}
```