tustvold commented on code in PR #2297:
URL: https://github.com/apache/arrow-rs/pull/2297#discussion_r936536117
##########
arrow/src/array/array_dictionary.rs:
##########
@@ -385,6 +404,86 @@ impl<T: ArrowPrimitiveType> fmt::Debug for
DictionaryArray<T> {
}
}
+/// A strongly-typed wrapper around a [`DictionaryArray`] that implements
[`ArrayAccessor`]
+/// allowing fast access to its elements
+///
+/// ```
+/// use arrow::array::{ArrayIter, DictionaryArray, StringArray};
+/// use arrow::datatypes::Int32Type;
+///
+/// let orig = ["a", "b", "a", "b"];
+/// let dictionary = DictionaryArray::<Int32Type>::from_iter(orig);
+/// let typed = dictionary.downcast_dict::<StringArray>().unwrap();
+///
+/// for (maybe_val, orig) in typed.into_iter().zip(orig) {
+/// assert_eq!(maybe_val.unwrap(), orig)
+/// }
+/// ```
+#[derive(Copy, Clone)]
+pub struct TypedDictionaryArray<'a, K: ArrowPrimitiveType, V> {
+ /// The dictionary array
+ pub dictionary: &'a DictionaryArray<K>,
+ /// The values of the dictionary
+ pub values: &'a V,
+}
+
+impl<'a, K: ArrowPrimitiveType, V> fmt::Debug for TypedDictionaryArray<'a, K,
V> {
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ writeln!(f, "TypedDictionaryArray({:?})", self.dictionary)
+ }
+}
+
+impl<'a, K: ArrowPrimitiveType, V: Sync> Array for TypedDictionaryArray<'a, K,
V> {
+ fn as_any(&self) -> &dyn Any {
+ self.dictionary
+ }
+
+ fn data(&self) -> &ArrayData {
+ &self.dictionary.data
+ }
+
+ fn into_data(self) -> ArrayData {
+ self.dictionary.into_data()
+ }
+}
+
+impl<'a, K, V> IntoIterator for TypedDictionaryArray<'a, K, V>
+where
+ K: ArrowPrimitiveType,
+ V: Sync + Send,
+ &'a V: ArrayAccessor,
+{
+ type Item = Option<<Self as ArrayAccessor>::Item>;
+ type IntoIter = ArrayIter<Self>;
+
+ fn into_iter(self) -> Self::IntoIter {
+ ArrayIter::new(self)
Review Comment:
I think this is a nice example of how the composability of traits can be
better than macros
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