[GitHub] [arrow-rs] tustvold commented on a diff in pull request #3227: Zero out child null mask in new_null_array for StructArray

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

tustvold commented on code in PR #3227:
URL: https://github.com/apache/arrow-rs/pull/3227#discussion_r1034839270


##########
arrow-array/src/array/mod.rs:
##########
@@ -702,14 +702,31 @@ pub fn new_null_array(data_type: &DataType, length: usize) -> ArrayRef {
                 ],
             )
         }),
-        DataType::Struct(fields) => {
-            let fields: Vec<_> = fields
+        d @ DataType::Struct(fields) => {
+            let child_data = fields
                 .iter()
-                .map(|field| (field.clone(), new_null_array(field.data_type(), length)))
+                .map(|field| {
+                    // Nulls are encoded in the parent StructArray instead, otherwise this

Review Comment:
   This does create an interesting problem for dictionaries, where the resulting child data is technically ill-formed now. I'm not really sure what can be done about this



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