[GitHub] [arrow-rs] tustvold commented on a diff in pull request #1859: Omit validity buffer in PrimitiveArray::from_iter when all values are valid

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

tustvold commented on code in PR #1859:
URL: https://github.com/apache/arrow-rs/pull/1859#discussion_r895548001


##########
arrow/src/array/array_primitive.rs:
##########
@@ -397,29 +397,39 @@ impl<'a, T: ArrowPrimitiveType, Ptr: Into<NativeAdapter<T>>> FromIterator<Ptr>
         let iter = iter.into_iter();
         let (lower, _) = iter.size_hint();
 
-        let mut null_buf = BooleanBufferBuilder::new(lower);
+        let mut null_builder = BooleanBufferBuilder::new(lower);
 
         let buffer: Buffer = iter
             .map(|item| {
                 if let Some(a) = item.into().native {
-                    null_buf.append(true);
+                    null_builder.append(true);
                     a
                 } else {
-                    null_buf.append(false);
+                    null_builder.append(false);
                     // this ensures that null items on the buffer are not arbitrary.
-                    // This is important because falible operations can use null values (e.g. a vectorized "add")
+                    // This is important because fallible operations can use null values (e.g. a vectorized "add")
                     // which may panic (e.g. overflow if the number on the slots happen to be very large).
                     T::Native::default()
                 }
             })
             .collect();
 
+        let len = null_builder.len();
+        let null_buf: Buffer = null_builder.into();
+        let valid_count = null_buf.count_set_bits();
+        let null_count = len - valid_count;
+        let opt_null_buf = if null_count == 0 {
+            None
+        } else {
+            Some(null_buf)
+        };

Review Comment:
   ```suggestion
           let opt_null_buf = (null_count != 0).then(|| null_buf);
   ```



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