[GitHub] [arrow-rs] alamb commented on issue #1047: Add `Scalar` / `Datum` support to compute kernels

["alamb (via GitHub)" <gi...@apache.org>]

alamb commented on issue #1047:
URL: https://github.com/apache/arrow-rs/issues/1047#issuecomment-1572509590

   > Taking a step back I had a potentially controversial thought, why not just treat a single element array as a scalar array?
   
   For what it is worth I think this is what DuckDB does (at least this is how I interpret this slide from the  [22 - DuckDB Internals (CMU Advanced Databases / Spring 2023)](https://www.youtube.com/watch?v=bZOvAKGkzpQ) lecture
   
   
   <img width="589" alt="Screenshot 2023-06-01 at 1 30 17 PM" src="https://github.com/apache/arrow-rs/assets/490673/575dbc83-f32c-4d23-9b85-afea579a2576">
   
   I think the biggest potential downside of the "use a single row to mean a scalar value" could be that it is confusing as an API. The two input array sizes have to match *except* when one of them (would it always be the right argument?) had a single row, in which case it would have a special fast path 🤔 But it wouldn't be clear from the call signature if there was a special fast path or not. 
   
   
   
   ```
   enum Datum<'a> {
       Array(&'a dyn Array),
       Scalar(&'a dyn Scalar)
   }
   ``
   
   
   


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