tustvold commented on code in PR #3117:
URL: https://github.com/apache/arrow-rs/pull/3117#discussion_r1022291987
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arrow-array/src/cast.rs:
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@@ -550,6 +551,38 @@ array_downcast_fn!(as_union_array, UnionArray);
array_downcast_fn!(as_map_array, MapArray);
array_downcast_fn!(as_decimal_array, Decimal128Array);
+/// Downcasts a `dyn Array` to a concrete type
+///
+/// ```
+/// # use arrow_array::{BooleanArray, Int32Array, RecordBatch, StringArray};
+/// # use arrow_array::cast::downcast_array;
+/// struct ConcreteBatch {
+/// col1: Int32Array,
+/// col2: BooleanArray,
+/// col3: StringArray,
+/// }
+///
+/// impl ConcreteBatch {
+/// fn new(batch: &RecordBatch) -> Self {
+/// Self {
+/// col1: downcast_array(batch.column(0).as_ref()),
+/// col2: downcast_array(batch.column(1).as_ref()),
+/// col3: downcast_array(batch.column(2).as_ref()),
+/// }
+/// }
+/// }
+/// ```
+///
+/// # Panics
+///
+/// Panics if array is not of the correct data type
+pub fn downcast_array<T>(array: &dyn Array) -> T
+where
+ T: From<ArrayData>,
+{
+ T::from(array.data().clone())
Review Comment:
There may be some mechanism to avoid this clone, if/when we work this out
this can be optimised. In practice, this clone should be irrelevant, as it all
the underlying buffers are reference counted
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