alamb opened a new issue, #4517:
URL: https://github.com/apache/arrow-rs/issues/4517

   **Is your feature request related to a problem or challenge? Please describe 
what you are trying to do.**
   
   While implement unnest in DataFusion for FixedSizeListArray (see 
https://github.com/apache/arrow-datafusion/pull/6903) it turns out there is no 
support for `FixedSizeListArray` in the `length` kernel
   
   https://docs.rs/arrow/latest/arrow/compute/kernels/length/fn.length.html
   
   **Describe the solution you'd like**
   While it sounds silly, I would like to Support `FixedSizedListArray` for 
`length` kernel
   
   Specifically, it would be nice to get the NULLs handled correctly even 
though all the values will of course be the same (fixed!) size lenth
   
   Here is a reproducer:
   
   ```rust
   
   fn main() {
       // Construct a value array
       let value_data = ArrayData::builder(DataType::Int32)
           .len(9)
           .add_buffer(Buffer::from_slice_ref(&[0, 1, 2, 3, 4, 5, 6, 7, 8]))
           .build()
           .unwrap();
       let list_data_type = DataType::FixedSizeList(
           Arc::new(Field::new("item", DataType::Int32, false)),
           3,
       );
       let nulls = NullBuffer::from(vec![true, false, true]);
       let list_data = ArrayData::builder(list_data_type.clone())
           .len(3)
           .add_child_data(value_data.clone())
           .nulls(Some(nulls))
           .build()
           .unwrap();
       let list_array = FixedSizeListArray::from(list_data);
   
   
       let lengths = 
arrow::compute::kernels::length::length(&list_array).unwrap();
       println!("{}", pretty_format_columns("lengths", &[lengths]).unwrap());
   
   }
   ````
   
   It should print out `[3, null, 3]`
   
   
   **Describe alternatives you've considered**
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   **Additional context**
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