From 5014746ba4bc760e0ddfee1f8f665e855137d025 Mon Sep 17 00:00:00 2001
From: Andrew Lamb <andrew@nerdnetworks.org>
Date: Thu, 15 Jan 2026 08:08:32 -0500
Subject: [PATCH] Avoid a clone when creating `MapArray` from ArrayData

---
 arrow-array/src/array/map_array.rs | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/arrow-array/src/array/map_array.rs b/arrow-array/src/array/map_array.rs
index 86608d586f34..02f9a35eb627 100644
--- a/arrow-array/src/array/map_array.rs
+++ b/arrow-array/src/array/map_array.rs
@@ -15,7 +15,7 @@
 // specific language governing permissions and limitations
 // under the License.
 
-use crate::array::{get_offsets, print_long_array};
+use crate::array::{get_offsets_from_buffer, print_long_array};
 use crate::iterator::MapArrayIter;
 use crate::{Array, ArrayAccessor, ArrayRef, ListArray, StringArray, StructArray, make_array};
 use arrow_buffer::{ArrowNativeType, Buffer, NullBuffer, OffsetBuffer, ToByteSlice};
@@ -272,28 +272,29 @@ impl From<MapArray> for ArrayData {
 
 impl MapArray {
     fn try_new_from_array_data(data: ArrayData) -> Result<Self, ArrowError> {
-        if !matches!(data.data_type(), DataType::Map(_, _)) {
+        let (data_type, len, nulls, offset, mut buffers, mut child_data) = data.into_parts();
+
+        if !matches!(data_type, DataType::Map(_, _)) {
             return Err(ArrowError::InvalidArgumentError(format!(
-                "MapArray expected ArrayData with DataType::Map got {}",
-                data.data_type()
+                "MapArray expected ArrayData with DataType::Map got {data_type}",
             )));
         }
 
-        if data.buffers().len() != 1 {
+        if buffers.len() != 1 {
             return Err(ArrowError::InvalidArgumentError(format!(
                 "MapArray data should contain a single buffer only (value offsets), had {}",
-                data.len()
+                buffers.len(),
             )));
         }
+        let buffer = buffers.pop().expect("checked above");
 
-        if data.child_data().len() != 1 {
+        if child_data.len() != 1 {
             return Err(ArrowError::InvalidArgumentError(format!(
                 "MapArray should contain a single child array (values array), had {}",
-                data.child_data().len()
+                child_data.len()
             )));
         }
-
-        let entries = data.child_data()[0].clone();
+        let entries = child_data.pop().expect("checked above");
 
         if let DataType::Struct(fields) = entries.data_type() {
             if fields.len() != 2 {
@@ -312,11 +313,11 @@ impl MapArray {
 
         // SAFETY:
         // ArrayData is valid, and verified type above
-        let value_offsets = unsafe { get_offsets(&data) };
+        let value_offsets = unsafe { get_offsets_from_buffer(buffer, offset, len) };
 
         Ok(Self {
-            data_type: data.data_type().clone(),
-            nulls: data.nulls().cloned(),
+            data_type,
+            nulls,
             entries,
             value_offsets,
         })