[GitHub] [arrow-rs] tustvold commented on a diff in pull request #2247: Impl FromIterator for Decimal256Array

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

tustvold commented on code in PR #2247:
URL: https://github.com/apache/arrow-rs/pull/2247#discussion_r933943533


##########
arrow/src/array/array_decimal.rs:
##########
@@ -384,6 +391,59 @@ impl<'a> Decimal128Array {
     }
 }
 
+impl From<BigInt> for Decimal256 {
+    fn from(bigint: BigInt) -> Self {
+        Decimal256::from_big_int(&bigint, DECIMAL256_MAX_PRECISION, DECIMAL_DEFAULT_SCALE)
+            .unwrap()
+    }
+}
+
+fn build_decimal_array_from<U: BasicDecimalArray<T, U>, T>(
+    null_buf: BooleanBufferBuilder,
+    buffer: Buffer,
+) -> U
+where
+    T: BasicDecimal,
+    U: From<ArrayData>,
+{
+    let data = unsafe {
+        ArrayData::new_unchecked(
+            U::default_type(),
+            null_buf.len(),
+            None,
+            Some(null_buf.into()),
+            0,
+            vec![buffer],
+            vec![],
+        )
+    };
+    U::from(data)
+}
+
+impl<Ptr: Into<Decimal256>> FromIterator<Option<Ptr>> for Decimal256Array {
+    fn from_iter<I: IntoIterator<Item = Option<Ptr>>>(iter: I) -> Self {
+        let iter = iter.into_iter();
+        let (lower, upper) = iter.size_hint();
+        let size_hint = upper.unwrap_or(lower);
+
+        let mut null_buf = BooleanBufferBuilder::new(size_hint);
+
+        let mut buffer = MutableBuffer::from_len_zeroed(0);

Review Comment:
   It might be better to create this with the required capacity (not zero-ed) up front



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