reshape view doesn't infer shape from -1

[JosephSummerhays1]

#926

behold my code:

int main() {                   
    xt::xarray<float> a = xt::zeros<float>({3, 3, 3});
    auto b = xt::reshape_view(a, {3, -1});
    cout << xt::adapt(a.shape()) << endl;
    cout << xt::adapt(b.shape()) << endl;
}

and it's unexpected output

{3, 3, 3}
{                   3, 18446744073709551615}

While nowhere in the documentation does it claim to handle -1 as numpy does, and this is probably just my fault for assuming this, it would be very convenient if it did.

[tdegeus]

As method reshape seems to support having one entry -1, see docs. In my opinion reshape_view should also support this. However, in your case -1 seems to be casted to a signed integer. So I think this is a bug. But maybe others disagree?

[spectre-ns]

@tdegeus I agree with @JosephSummerhays1 I've done this several times and it's a nightmare to find when xt::xarray<T>::reshape does it. I also find myself doing xt::reshape_view(data, {data.size() / lastAxisLength, lastAxisLength}) this is pretty ugly.