[GitHub] [arrow-rs] alamb commented on a diff in pull request #4263: Add constructors for FixedSize array types (#3879)

["alamb (via GitHub)" <gi...@apache.org>]

alamb commented on code in PR #4263:
URL: https://github.com/apache/arrow-rs/pull/4263#discussion_r1204686679


##########
arrow-array/src/array/fixed_size_list_array.rs:
##########
@@ -68,6 +69,114 @@ pub struct FixedSizeListArray {
 }
 
 impl FixedSizeListArray {
+    /// Create a new [`FixedSizeListArray`] with `size` element size, panicking on failure
+    ///
+    /// # Panics
+    ///
+    /// Panics if [`Self::try_new`] returns an error
+    pub fn new(
+        field: FieldRef,
+        size: i32,
+        values: ArrayRef,
+        nulls: Option<NullBuffer>,
+    ) -> Self {
+        Self::try_new(field, size, values, nulls).unwrap()
+    }
+
+    /// Create a new [`FixedSizeListArray`] from the provided parts, returning an error on failure
+    ///
+    /// # Errors
+    ///
+    /// * `size < 0`
+    /// * `values.len() / size != nulls.len()`
+    /// * `values.data_type() != field.data_type()`
+    /// * `!field.is_nullable() && !nulls.expand(size).contains(values.nulls())`
+    pub fn try_new(
+        field: FieldRef,
+        size: i32,

Review Comment:
   I think naming this parameter `value_length` to align with the field name would make it easier to understand



##########
arrow-data/src/data/mod.rs:
##########
@@ -1152,40 +1151,17 @@ impl ArrayData {
                     match &self.nulls {
                         Some(nulls) => {
                             let element_len = *len as usize;
-                            let mut buffer =
-                                MutableBuffer::new_null(element_len * self.len);
-
-                            // Expand each bit within `null_mask` into `element_len`
-                            // bits, constructing the implicit mask of the child elements
-                            for i in 0..self.len {
-                                if nulls.is_null(i) {
-                                    continue;
-                                }
-                                for j in 0..element_len {
-                                    bit_util::set_bit(
-                                        buffer.as_mut(),
-                                        i * element_len + j,
-                                    )
-                                }
-                            }
-                            let mask = buffer.into();
-                            self.validate_non_nullable(Some(&mask), 0, child)?;
+                            let expanded = nulls.expand(element_len);

Review Comment:
   this is a nice cleanup



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