Add ArrayAccessor trait (#1948)

arrow/src/array/array.rs

@@ -297,6 +297,79 @@ impl Array for ArrayRef {
     }
 }
 
+impl<'a, T: Array> Array for &'a T {
+    fn as_any(&self) -> &dyn Any {
+        T::as_any(self)
+    }
+
+    fn data(&self) -> &ArrayData {
+        T::data(self)
+    }
+
+    fn into_data(self) -> ArrayData {
+        self.data().clone()
+    }
+
+    fn data_ref(&self) -> &ArrayData {
+        T::data_ref(self)
+    }
+
+    fn data_type(&self) -> &DataType {
+        T::data_type(self)
+    }
+
+    fn slice(&self, offset: usize, length: usize) -> ArrayRef {
+        T::slice(self, offset, length)
+    }
+
+    fn len(&self) -> usize {
+        T::len(self)
+    }
+
+    fn is_empty(&self) -> bool {
+        T::is_empty(self)
+    }
+
+    fn offset(&self) -> usize {
+        T::offset(self)
+    }
+
+    fn is_null(&self, index: usize) -> bool {
+        T::is_null(self, index)
+    }
+
+    fn is_valid(&self, index: usize) -> bool {
+        T::is_valid(self, index)
+    }
+
+    fn null_count(&self) -> usize {
+        T::null_count(self)
+    }
+
+    fn get_buffer_memory_size(&self) -> usize {
+        T::get_buffer_memory_size(self)
+    }
+
+    fn get_array_memory_size(&self) -> usize {
+        T::get_array_memory_size(self)
+    }
+
+    fn to_raw(
+        &self,
+    ) -> Result<(*const ffi::FFI_ArrowArray, *const ffi::FFI_ArrowSchema)> {
+        T::to_raw(self)
+    }
+}
+
+/// A generic trait for accessing the values of an [`Array`]
+pub trait ArrayAccessor: Array {
+    type Item: Send + Sync;
+
+    fn value(&self, index: usize) -> Self::Item;
+
+    unsafe fn value_unchecked(&self, index: usize) -> Self::Item;
+}
+
 /// Constructs an array using the input `data`.
 /// Returns a reference-counted `Array` instance.
 pub fn make_array(data: ArrayData) -> ArrayRef {

arrow/src/array/array_binary.rs

@@ -23,6 +23,7 @@ use super::{
     array::print_long_array, raw_pointer::RawPtrBox, Array, ArrayData,
     FixedSizeListArray, GenericBinaryIter, GenericListArray, OffsetSizeTrait,
 };
+use crate::array::array::ArrayAccessor;
 pub use crate::array::DecimalIter;
 use crate::buffer::Buffer;
 use crate::error::{ArrowError, Result};
@@ -245,6 +246,20 @@ impl<OffsetSize: OffsetSizeTrait> Array for GenericBinaryArray<OffsetSize> {
     }
 }
 
+impl<'a, OffsetSize: OffsetSizeTrait> ArrayAccessor
+    for &'a GenericBinaryArray<OffsetSize>
+{
+    type Item = &'a [u8];
+
+    fn value(&self, index: usize) -> Self::Item {
+        GenericBinaryArray::value(self, index)
+    }
+
+    unsafe fn value_unchecked(&self, index: usize) -> Self::Item {
+        GenericBinaryArray::value_unchecked(self, index)
+    }
+}
+
 impl<OffsetSize: OffsetSizeTrait> From<ArrayData> for GenericBinaryArray<OffsetSize> {
     fn from(data: ArrayData) -> Self {
         assert_eq!(

arrow/src/array/array_boolean.rs

@@ -15,6 +15,7 @@
 // specific language governing permissions and limitations
 // under the License.
 
+use crate::array::array::ArrayAccessor;
 use std::borrow::Borrow;
 use std::convert::From;
 use std::iter::{FromIterator, IntoIterator};
@@ -157,6 +158,18 @@ impl Array for BooleanArray {
     }
 }
 
+impl<'a> ArrayAccessor for &'a BooleanArray {
+    type Item = bool;
+
+    fn value(&self, index: usize) -> Self::Item {
+        BooleanArray::value(self, index)
+    }
+
+    unsafe fn value_unchecked(&self, index: usize) -> Self::Item {
+        BooleanArray::value_unchecked(self, index)
+    }
+}
+
 impl From<Vec<bool>> for BooleanArray {
     fn from(data: Vec<bool>) -> Self {
         let mut mut_buf = MutableBuffer::new_null(data.len());

arrow/src/array/array_list.rs

@@ -24,6 +24,7 @@ use super::{
     array::print_long_array, make_array, raw_pointer::RawPtrBox, Array, ArrayData,
     ArrayRef, BooleanBufferBuilder, GenericListArrayIter, PrimitiveArray,
 };
+use crate::array::array::ArrayAccessor;
 use crate::{
     buffer::MutableBuffer,
     datatypes::{ArrowNativeType, ArrowPrimitiveType, DataType, Field},
@@ -245,7 +246,7 @@ impl<OffsetSize: OffsetSizeTrait> GenericListArray<OffsetSize> {
     }
 }
 
-impl<OffsetSize: 'static + OffsetSizeTrait> Array for GenericListArray<OffsetSize> {
+impl<OffsetSize: OffsetSizeTrait> Array for GenericListArray<OffsetSize> {
     fn as_any(&self) -> &dyn Any {
         self
     }
@@ -259,6 +260,18 @@ impl<OffsetSize: 'static + OffsetSizeTrait> Array for GenericListArray<OffsetSiz
     }
 }
 
+impl<'a, OffsetSize: OffsetSizeTrait> ArrayAccessor for &'a GenericListArray<OffsetSize> {
+    type Item = ArrayRef;
+
+    fn value(&self, index: usize) -> Self::Item {
+        GenericListArray::value(self, index)
+    }
+
+    unsafe fn value_unchecked(&self, index: usize) -> Self::Item {
+        GenericListArray::value(self, index)
+    }
+}
+
 impl<OffsetSize: OffsetSizeTrait> fmt::Debug for GenericListArray<OffsetSize> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         let prefix = if OffsetSize::IS_LARGE { "Large" } else { "" };
@@ -466,6 +479,18 @@ impl Array for FixedSizeListArray {
     }
 }
 
+impl ArrayAccessor for FixedSizeListArray {
+    type Item = ArrayRef;
+
+    fn value(&self, index: usize) -> Self::Item {
+        FixedSizeListArray::value(self, index)
+    }
+
+    unsafe fn value_unchecked(&self, index: usize) -> Self::Item {
+        FixedSizeListArray::value(self, index)
+    }
+}
+
 impl fmt::Debug for FixedSizeListArray {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f, "FixedSizeListArray<{}>\n[\n", self.value_length())?;

arrow/src/array/array_primitive.rs

@@ -33,6 +33,7 @@ use crate::{
     util::trusted_len_unzip,
 };
 
+use crate::array::array::ArrayAccessor;
 use half::f16;
 
 /// Array whose elements are of primitive types.
@@ -188,6 +189,18 @@ impl<T: ArrowPrimitiveType> Array for PrimitiveArray<T> {
     }
 }
 
+impl<'a, T: ArrowPrimitiveType> ArrayAccessor for &'a PrimitiveArray<T> {
+    type Item = T::Native;
+
+    fn value(&self, index: usize) -> Self::Item {
+        PrimitiveArray::value(self, index)
+    }
+
+    unsafe fn value_unchecked(&self, index: usize) -> Self::Item {
+        PrimitiveArray::value_unchecked(self, index)
+    }
+}
+
 fn as_datetime<T: ArrowPrimitiveType>(v: i64) -> Option<NaiveDateTime> {
     match T::DATA_TYPE {
         DataType::Date32 => Some(temporal_conversions::date32_to_datetime(v as i32)),

arrow/src/array/array_string.rs

@@ -23,6 +23,7 @@ use super::{
     array::print_long_array, raw_pointer::RawPtrBox, Array, ArrayData, GenericListArray,
     GenericStringIter, OffsetSizeTrait,
 };
+use crate::array::array::ArrayAccessor;
 use crate::buffer::Buffer;
 use crate::util::bit_util;
 use crate::{buffer::MutableBuffer, datatypes::DataType};
@@ -298,6 +299,20 @@ impl<OffsetSize: OffsetSizeTrait> Array for GenericStringArray<OffsetSize> {
     }
 }
 
+impl<'a, OffsetSize: OffsetSizeTrait> ArrayAccessor
+    for &'a GenericStringArray<OffsetSize>
+{
+    type Item = &'a str;
+
+    fn value(&self, index: usize) -> Self::Item {
+        GenericStringArray::value(self, index)
+    }
+
+    unsafe fn value_unchecked(&self, index: usize) -> Self::Item {
+        GenericStringArray::value_unchecked(self, index)
+    }
+}
+
 impl<OffsetSize: OffsetSizeTrait> From<ArrayData> for GenericStringArray<OffsetSize> {
     fn from(data: ArrayData) -> Self {
         assert_eq!(

arrow/src/array/equal_json.rs

@@ -37,6 +37,16 @@ pub trait JsonEqual {
     }
 }
 
+impl<'a, T: JsonEqual> JsonEqual for &'a T {
+    fn equals_json(&self, json: &[&Value]) -> bool {
+        T::equals_json(self, json)
+    }
+
+    fn equals_json_values(&self, json: &[Value]) -> bool {
+        T::equals_json_values(self, json)
+    }
+}
+
 /// Implement array equals for numeric type
 impl<T: ArrowPrimitiveType> JsonEqual for PrimitiveArray<T> {
     fn equals_json(&self, json: &[&Value]) -> bool {