[GitHub] [arrow] mcassels commented on a change in pull request #6770: ARROW-7842: [Rust] [Parquet] implement array_reader for list type columns

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

mcassels commented on a change in pull request #6770:
URL: https://github.com/apache/arrow/pull/6770#discussion_r419189845



##########
File path: rust/parquet/src/arrow/array_reader.rs
##########
@@ -468,6 +491,391 @@ where
     }
 }
 
+/// Implementation of list array reader.
+pub struct ListArrayReader {
+    item_reader: Box<dyn ArrayReader>,
+    data_type: ArrowType,
+    item_type: ArrowType,
+    list_def_level: i16,
+    list_rep_level: i16,
+    def_level_buffer: Option<Buffer>,
+    rep_level_buffer: Option<Buffer>,
+}
+
+impl ListArrayReader {
+    /// Construct list array reader.
+    pub fn new(
+        item_reader: Box<dyn ArrayReader>,
+        data_type: ArrowType,
+        item_type: ArrowType,
+        def_level: i16,
+        rep_level: i16,
+    ) -> Self {
+        Self {
+            item_reader,
+            data_type,
+            item_type,
+            list_def_level: def_level,
+            list_rep_level: rep_level,
+            def_level_buffer: None,
+            rep_level_buffer: None,
+        }
+    }
+}
+
+macro_rules! build_empty_list_array_with_primitive_items {
+    ($item_type:ident) => {{
+        let values_builder = PrimitiveBuilder::<$item_type>::new(0);
+        let mut builder = ListBuilder::new(values_builder);
+        let empty_list_array = builder.finish();
+        Ok(Arc::new(empty_list_array))
+    }};
+}
+
+macro_rules! build_empty_list_array_with_non_primitive_items {
+    ($builder:ident) => {{
+        let values_builder = $builder::new(0);
+        let mut builder = ListBuilder::new(values_builder);
+        let empty_list_array = builder.finish();
+        Ok(Arc::new(empty_list_array))
+    }};
+}
+
+fn build_empty_list_array(item_type: ArrowType) -> Result<ArrayRef> {
+    match item_type {
+        ArrowType::UInt8 => build_empty_list_array_with_primitive_items!(ArrowUInt8Type),
+        ArrowType::UInt16 => {
+            build_empty_list_array_with_primitive_items!(ArrowUInt16Type)
+        }
+        ArrowType::UInt32 => {
+            build_empty_list_array_with_primitive_items!(ArrowUInt32Type)
+        }
+        ArrowType::UInt64 => {
+            build_empty_list_array_with_primitive_items!(ArrowUInt64Type)
+        }
+        ArrowType::Int8 => build_empty_list_array_with_primitive_items!(ArrowInt8Type),
+        ArrowType::Int16 => build_empty_list_array_with_primitive_items!(ArrowInt16Type),
+        ArrowType::Int32 => build_empty_list_array_with_primitive_items!(ArrowInt32Type),
+        ArrowType::Int64 => build_empty_list_array_with_primitive_items!(ArrowInt64Type),
+        ArrowType::Float32 => {
+            build_empty_list_array_with_primitive_items!(ArrowFloat32Type)
+        }
+        ArrowType::Float64 => {
+            build_empty_list_array_with_primitive_items!(ArrowFloat64Type)
+        }
+        ArrowType::Boolean => {
+            build_empty_list_array_with_primitive_items!(ArrowBooleanType)
+        }
+        ArrowType::Date32(_) => {
+            build_empty_list_array_with_primitive_items!(ArrowDate32Type)
+        }
+        ArrowType::Date64(_) => {
+            build_empty_list_array_with_primitive_items!(ArrowDate64Type)
+        }
+        ArrowType::Time32(ArrowTimeUnit::Second) => {
+            build_empty_list_array_with_primitive_items!(ArrowTime32SecondType)
+        }
+        ArrowType::Time32(ArrowTimeUnit::Millisecond) => {
+            build_empty_list_array_with_primitive_items!(ArrowTime32MillisecondType)
+        }
+        ArrowType::Time64(ArrowTimeUnit::Microsecond) => {
+            build_empty_list_array_with_primitive_items!(ArrowTime64MicrosecondType)
+        }
+        ArrowType::Time64(ArrowTimeUnit::Nanosecond) => {
+            build_empty_list_array_with_primitive_items!(ArrowTime64NanosecondType)
+        }
+        ArrowType::Duration(ArrowTimeUnit::Second) => {

Review comment:
       It looks like the PrimitiveArrayReader implementation [supports Duration] (https://github.com/apache/arrow/blob/master/rust/parquet/src/arrow/array_reader.rs#L206)




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