jorgecarleitao edited a comment on pull request #9301:
URL: https://github.com/apache/arrow/pull/9301#issuecomment-766163142


   Now I get your point. On the PR description, I mention to _independent_ 
sources of unsoundness:
   
   * we are using indices from null slots
   * we are not performing bound checks on values.
   
   In particular, the second point above allows the following code to run with 
exit 0:
   
   ```rust
       #[test]
       fn test_bla() {
           let indices = UInt32Array::from(vec![1, 10, 1000, 100000]);
   
           let values = UInt32Array::from(vec![0, 1, 2, 3]);
           let r = take(&values, &indices, None).unwrap();
           println!("{:?}", r);
       }
   ```
   
   which of course gives a meaningless result, but demonstrates the issue here: 
this code is marked as `safe` but is UB.


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