Re: How to obtain Variant underlying type?

[jfondren via Digitalmars-d-learn]

On Saturday, 9 July 2022 at 23:04:20 UTC, anonymouse wrote:

On Saturday, 9 July 2022 at 14:46:36 UTC, Adam D Ruppe wrote:

Impossible; Variant's type is only known at runtime, and this would require compile time knowledge.

Hmmm. Okay, thanks. What I really need to know is how many dimensions an array has and the total elements per dimension so that I can create temporary storage for it later.

     this(T)(T a)
     in(imported!"std.traits".isDynamic!T)
     {
         data = a; // data is of type Variant

shape = [a.length, {?, ...}]; // what's the best way to deterine?

     }

Thanks,
--anonymouse

```d
import std.variant : Variant;

size_t[] shape(Variant v) {
    import std.variant : VariantException;

    size_t[] s;
    try {
        while (true) {
            Variant elem = v[0];
            s ~= v.length;
            v = elem;
        }
    } catch (VariantException e) {
        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);

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