Method pack

src/expr/src/scalar/func/impls/array.rs:133–160

(
            temp_storage: &RowArena,
            elems: &mut impl Iterator<Item = Datum<'a>>,
            dims: &[ArrayDimension],
            cast_element: &MirScalarExpr,
            packer: &mut 

        a: &'a impl Eval,
    ) -> Result<Datum<'a>, EvalError> {
        fn pack<'a>(
            temp_storage: &RowArena,
            elems: &mut impl Iterator<Item = Datum<'a>>,
            dims: &[ArrayDimension],
            cast_element: &MirScalarExpr,
            packer: &mut RowPacker,
        ) -> Result<(), EvalError> {
            packer.push_list_with(|packer| match dims {
                [] => Ok(()),
                [dim] => {
                    for _ in 0..dim.length {
                        let elem = elems.next().unwrap();
                        let elem = match cast_element.eval(&[elem], temp_storage)? {
                            Datum::Null => Datum::JsonNull,
                            d => d,
                        };
                        packer.push(elem);
                    }
                    Ok(())
                }
                [dim, rest @ ..] => {
                    for _ in 0..dim.length {
                        pack(temp_storage, elems, rest, cast_element, packer)?;
                    }
                    Ok(())
                }
            })
        }

        let a = a.eval(datums, temp_storage)?;
        if a.is_null() {