[GitHub] [arrow] alamb commented on a change in pull request #8852: ARROW-10826: [Rust] Add support for FixedSizeBinaryArray to MutableArrayData

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

alamb commented on a change in pull request #8852:
URL: https://github.com/apache/arrow/pull/8852#discussion_r537025118



##########
File path: rust/arrow/src/array/transform/mod.rs
##########
@@ -687,4 +690,24 @@ mod tests {
         let expected = Int16Array::from(vec![Some(1), None]);
         assert_eq!(result.keys(), &expected);
     }
+
+    #[test]
+    fn test_binary_fixed_sized_offsets() {
+        let array =
+            FixedSizeBinaryArray::from(vec![vec![0, 0], vec![0, 1], vec![0, 2]]).data();
+        let array = array.slice(1, 2);
+
+        let arrays = vec![&array];
+
+        let mut mutable = MutableArrayData::new(arrays, false, 0);
+
+        mutable.extend(0, 1, 2);
+        mutable.extend(0, 0, 1);
+
+        let result = mutable.freeze();
+        let result = FixedSizeBinaryArray::from(Arc::new(result));
+
+        let expected = FixedSizeBinaryArray::from(vec![vec![0, 2], vec![0, 1]]);

Review comment:
       I am having trouble figuring out why this is the expected output. I expected something like
   
   ```
           let expected = FixedSizeBinaryArray::from(vec![vec![0, 1], vec![0, 0]]);
   ```
   
   As I read 
   
   ```
           mutable.extend(0, 1, 2); // --> pick element 1 (aka vec[0, 1])
           mutable.extend(0, 0, 1); // --> pick element 0 (aka vec[0, 0])
   ```




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