Add MutableArray::as_box

This basically just changes the impls of `as_arc` to `as_box` and uses
the `From<Box<T>> for Arc<T>` impl to provide a default implementation
for `as_arc`.

src/array/binary/mutable.rs

@@ -146,8 +146,8 @@ impl<O: Offset> MutableArray for MutableBinaryArray<O> {
         &self.validity
     }
 
-    fn as_arc(&mut self) -> Arc<dyn Array> {
-        Arc::new(BinaryArray::from_data(
+    fn as_box(&mut self) -> Box<dyn Array> {
+        Box::new(BinaryArray::from_data(
             self.data_type.clone(),
             std::mem::take(&mut self.offsets).into(),
             std::mem::take(&mut self.values).into(),

src/array/boolean/mutable.rs

@@ -338,8 +338,8 @@ impl MutableArray for MutableBooleanArray {
         &self.validity
     }
 
-    fn as_arc(&mut self) -> Arc<dyn Array> {
-        Arc::new(BooleanArray::from_data(
+    fn as_box(&mut self) -> Box<dyn Array> {
+        Box::new(BooleanArray::from_data(
             self.data_type.clone(),
             std::mem::take(&mut self.values).into(),
             std::mem::take(&mut self.validity).map(|x| x.into()),

src/array/dictionary/mutable.rs

@@ -115,8 +115,8 @@ impl<K: DictionaryKey, M: 'static + MutableArray> MutableArray for MutableDictio
         self.keys.validity()
     }
 
-    fn as_arc(&mut self) -> Arc<dyn Array> {
-        Arc::new(DictionaryArray::<K>::from_data(
+    fn as_box(&mut self) -> Box<dyn Array> {
+        Box::new(DictionaryArray::<K>::from_data(
             std::mem::take(&mut self.keys).into(),
             self.values.as_arc(),
         ))

src/array/fixed_size_binary/mutable.rs

@@ -1,5 +1,3 @@
-use std::sync::Arc;
-
 use crate::{
     array::{Array, MutableArray},
     bitmap::MutableBitmap,
@@ -173,8 +171,8 @@ impl MutableArray for MutableFixedSizeBinaryArray {
         &self.validity
     }
 
-    fn as_arc(&mut self) -> Arc<dyn Array> {
-        Arc::new(FixedSizeBinaryArray::from_data(
+    fn as_box(&mut self) -> Box<dyn Array> {
+        Box::new(FixedSizeBinaryArray::from_data(
             DataType::FixedSizeBinary(self.size as i32),
             std::mem::take(&mut self.values).into(),
             std::mem::take(&mut self.validity).map(|x| x.into()),

src/array/fixed_size_list/mutable.rs

@@ -1,5 +1,3 @@
-use std::sync::Arc;
-
 use crate::{
     array::{
         Array, MutableArray, MutableBinaryArray, MutablePrimitiveArray, MutableUtf8Array, Offset,
@@ -69,8 +67,8 @@ impl<M: MutableArray + 'static> MutableArray for MutableFixedSizeListArray<M> {
         &self.validity
     }
 
-    fn as_arc(&mut self) -> Arc<dyn Array> {
-        Arc::new(FixedSizeListArray::from_data(
+    fn as_box(&mut self) -> Box<dyn Array> {
+        Box::new(FixedSizeListArray::from_data(
             self.data_type.clone(),
             self.values.as_arc(),
             std::mem::take(&mut self.validity).map(|x| x.into()),

src/array/list/mutable.rs

@@ -177,8 +177,8 @@ impl<O: Offset, M: MutableArray + 'static> MutableArray for MutableListArray<O,
         &self.validity
     }
 
-    fn as_arc(&mut self) -> Arc<dyn Array> {
-        Arc::new(ListArray::from_data(
+    fn as_box(&mut self) -> Box<dyn Array> {
+        Box::new(ListArray::from_data(
             self.data_type.clone(),
             std::mem::take(&mut self.offsets).into(),
             self.values.as_arc(),

src/array/mod.rs

@@ -113,8 +113,13 @@ pub trait MutableArray: std::fmt::Debug {
     /// The optional validity of the array.
     fn validity(&self) -> &Option<MutableBitmap>;
 
-    /// Convert itself to an (immutable) [`Array`].
-    fn as_arc(&mut self) -> Arc<dyn Array>;
+    /// Convert itself to an (immutable) ['Array'].
+    fn as_box(&mut self) -> Box<dyn Array>;
+
+    /// Convert itself to an (immutable) atomically reference counted [`Array`].
+    fn as_arc(&mut self) -> Arc<dyn Array> {
+        self.as_box().into()
+    }
 
     /// Convert to `Any`, to enable dynamic casting.
     fn as_any(&self) -> &dyn Any;

src/array/primitive/mutable.rs

@@ -326,8 +326,8 @@ impl<T: NativeType> MutableArray for MutablePrimitiveArray<T> {
         &self.validity
     }
 
-    fn as_arc(&mut self) -> Arc<dyn Array> {
-        Arc::new(PrimitiveArray::from_data(
+    fn as_box(&mut self) -> Box<dyn Array> {
+        Box::new(PrimitiveArray::from_data(
             self.data_type.clone(),
             std::mem::take(&mut self.values).into(),
             std::mem::take(&mut self.validity).map(|x| x.into()),

src/array/utf8/mutable.rs

@@ -187,8 +187,8 @@ impl<O: Offset> MutableArray for MutableUtf8Array<O> {
         &self.validity
     }
 
-    fn as_arc(&mut self) -> Arc<dyn Array> {
-        Arc::new(Utf8Array::from_data(
+    fn as_box(&mut self) -> Box<dyn Array> {
+        Box::new(Utf8Array::from_data(
             Self::default_data_type(),
             std::mem::take(&mut self.offsets).into(),
             std::mem::take(&mut self.values).into(),