[GitHub] [arrow] Dandandan commented on a change in pull request #8829: ARROW-10804: Removed unsafe from parquet, causing a compilation error.

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

Dandandan commented on a change in pull request #8829:
URL: https://github.com/apache/arrow/pull/8829#discussion_r537870768



##########
File path: rust/parquet/src/arrow/record_reader.rs
##########
@@ -340,42 +297,41 @@ impl<T: DataType> RecordReader<T> {
         }
 
         // Convert mutable buffer spaces to mutable slices
-        let mut values_buf = FatPtr::<T::T>::with_offset_and_size(
-            &mut self.records,
-            self.values_written,
-            T::get_type_size(),
-        );
+        let (prefix, values, suffix) = unsafe { self.records.data_mut().align_to_mut::<T::T>() };
+        assert!(prefix.is_empty() && suffix.is_empty());
+        let values = &mut values[self.values_written..];
 
         let values_written = self.values_written;
-        let mut def_levels_buf = self
+        let def_levels = self
             .def_levels
             .as_mut()
-            .map(|buf| FatPtr::<i16>::with_offset(buf, values_written));
+            .map(|buf| {
+                let (prefix, values, suffix) = unsafe { buf.data_mut().align_to_mut::<i16>() };
+                assert!(prefix.is_empty() && suffix.is_empty());
+                &mut values[values_written..]
+            });
 
-        let mut rep_levels_buf = self
+        let rep_levels = self
             .rep_levels
             .as_mut()
-            .map(|buf| FatPtr::<i16>::with_offset(buf, values_written));
+            .map(|buf| {
+                let (prefix, values, suffix) = unsafe { buf.data_mut().align_to_mut::<i16>() };
+                assert!(prefix.is_empty() && suffix.is_empty());
+                &mut values[values_written..]
+            });
 
         let (values_read, levels_read) =
             self.column_reader.as_mut().unwrap().read_batch(
                 batch_size,
-                def_levels_buf.as_mut().map(|ptr| ptr.to_slice_mut()),
-                rep_levels_buf.as_mut().map(|ptr| ptr.to_slice_mut()),
-                values_buf.to_slice_mut(),
+                def_levels,

Review comment:
       The error originates from here, the error shows that it is moved here. A clone likely "solves" the issue? Usually taking the value by `&` in the function also solves this as it will stop it from taking ownership?




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