[GitHub] [arrow-rs] viirya commented on a diff in pull request #3961: feat: cast between `Binary`/`LargeBinary` and `FixedSizeBinary`

["viirya (via GitHub)" <gi...@apache.org>]

viirya commented on code in PR #3961:
URL: https://github.com/apache/arrow-rs/pull/3961#discussion_r1149575987


##########
arrow-cast/src/cast.rs:
##########
@@ -3390,6 +3405,63 @@ fn cast_binary_to_string<O: OffsetSizeTrait>(
     }
 }
 
+/// Helper function to cast from one `BinaryArray` or 'LargeBinaryArray' to 'FixedSizeBinaryArray'.
+fn cast_binary_to_fixed_size_binary<O: OffsetSizeTrait>(
+    array: &dyn Array,
+    byte_width: i32,
+) -> Result<ArrayRef, ArrowError> {
+    let array = array
+        .as_any()
+        .downcast_ref::<GenericBinaryArray<O>>()
+        .unwrap();
+
+    let mut builder = FixedSizeBinaryBuilder::with_capacity(array.len(), byte_width);
+
+    for i in 0..array.len() {
+        if array.is_null(i) {
+            builder.append_null();
+        } else {
+            builder.append_value(array.value(i))?;
+        }
+    }
+
+    Ok(Arc::new(builder.finish()))
+}
+
+/// Helper function to cast from 'FixedSizeBinaryArray' to one `BinaryArray` or 'LargeBinaryArray'.
+/// If the target one is too large for the source array it will return an Error.
+fn cast_fixed_size_binary_to_binary<O: OffsetSizeTrait>(
+    array: &dyn Array,
+    to_type: &DataType,
+    byte_width: i32,
+) -> Result<ArrayRef, ArrowError> {
+    let array = array
+        .as_any()
+        .downcast_ref::<FixedSizeBinaryArray>()
+        .unwrap();
+
+    let offsets: i64 = byte_width as i64 * array.len() as i64;
+
+    let is_binary = matches!(to_type, DataType::Binary);
+    if is_binary && offsets > i32::MAX as i64 {
+        return Err(ArrowError::ComputeError(
+            "Cast from FixedSizeBinary to Binary would overflow".to_string(),
+        ));
+    }

Review Comment:
   Isn't this also used to `LargeBinaryArray`?



##########
arrow-cast/src/cast.rs:
##########
@@ -3390,6 +3405,63 @@ fn cast_binary_to_string<O: OffsetSizeTrait>(
     }
 }
 
+/// Helper function to cast from one `BinaryArray` or 'LargeBinaryArray' to 'FixedSizeBinaryArray'.
+fn cast_binary_to_fixed_size_binary<O: OffsetSizeTrait>(
+    array: &dyn Array,
+    byte_width: i32,
+) -> Result<ArrayRef, ArrowError> {
+    let array = array
+        .as_any()
+        .downcast_ref::<GenericBinaryArray<O>>()
+        .unwrap();
+
+    let mut builder = FixedSizeBinaryBuilder::with_capacity(array.len(), byte_width);
+
+    for i in 0..array.len() {
+        if array.is_null(i) {
+            builder.append_null();
+        } else {
+            builder.append_value(array.value(i))?;
+        }
+    }
+
+    Ok(Arc::new(builder.finish()))
+}
+
+/// Helper function to cast from 'FixedSizeBinaryArray' to one `BinaryArray` or 'LargeBinaryArray'.
+/// If the target one is too large for the source array it will return an Error.
+fn cast_fixed_size_binary_to_binary<O: OffsetSizeTrait>(
+    array: &dyn Array,
+    to_type: &DataType,

Review Comment:
   `to_type` looks redundant as it is known `GenericBinaryType<O>`.



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