Additional operations on MutableListArray

[TethysSvensson]

It would be nice if there was a way to append one MutableListArray into another, which seems hard to do with the current API. This would ideally be both possible and efficient.

It would probably also be nice to be able to iterate over the values in the MutableListArray.

[TethysSvensson]

In case anybody else is looking for this, my current work-around is this:

fn extend<T: NativeType>(
    left: &mut MutableListArray<i64, MutablePrimitiveArray<T>>,
    right: &MutableListArray<i64, MutablePrimitiveArray<T>>,
) {
    left.mut_values().reserve(right.values().len());
    left.reserve(right.len());

    for offsets in ZipValidity::new(
        right.offsets().windows(2),
        right.validity().map(|v| v.iter()),
    ) {
        left.try_push(offsets.map(|offsets| {
            right
                .values()
                .iter()
                .skip(offsets[0] as usize)
                .take((offsets[1] - offsets[0]) as usize)
                .map(|v| v.copied())
        }))
        .unwrap();
    }
}

[jorgecarleitao]

I will try to find a way to address this. The root cause is that Rust without GAT is not particularly helpful for declaring variations of Vec (e.g. iter vs into_iter, TrustedLen), requiring some boilerplate to address all variations.

[jorgecarleitao]

@TethysSvensson , tried to address this in #1278.