[GitHub] [arrow-datafusion] retikulum commented on issue #3152: Improve codebase readability and error messages by and consistently handle downcasting

[GitBox <gi...@apache.org>]

retikulum commented on issue #3152:
URL: https://github.com/apache/arrow-datafusion/issues/3152#issuecomment-1292505183

   Hi. While this issue is getting old, I might help but have some questions. . I will give `as_int32_array` as a generic example so you can think of those questions for all other types.
   
   -  In which file we should implement `as_int32_array` function? I have implemented it in `datafusion\common\src\lib.rs` but I am not quite sure about the architecture.
   - Before opening pr, I want to be sure that this sample is implemented correctly. I added this function:
   ```rust
   pub fn as_int32_array(array: &dyn Array) -> Result<&Int32Array> {
       array.as_any().downcast_ref::<Int32Array>().ok_or(
         DataFusionError::Execution(format!("Expected a Int32Array, got: {}", array.data_type()),
       ))
   }
   ```
   And change this:
   https://github.com/apache/arrow-datafusion/blob/10e64dc013ba210ab1f6c2a3c02c66aef4a0e802/datafusion/optimizer/src/simplify_expressions/expr_simplifier.rs#L851-L854
   
   To this:
   ```rust
   let arg0 = as_int32_array(&args[0])?;
   ```
   Is this the correct way? [`simplify_expressions::test_evaluator_udfs`](https://github.com/apache/arrow-datafusion/blob/10e64dc013ba210ab1f6c2a3c02c66aef4a0e802/datafusion/optimizer/src/simplify_expressions/expr_simplifier.rs#L976) test runs successfully after implementation.


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