vegarsti commented on code in PR #8589:
URL: https://github.com/apache/arrow-rs/pull/8589#discussion_r2462584376
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arrow-cast/Cargo.toml:
##########
@@ -43,6 +43,7 @@ force_validate = []
arrow-array = { workspace = true }
arrow-buffer = { workspace = true }
arrow-data = { workspace = true }
+arrow-ord = { workspace = true }
Review Comment:
Does it suffice here to file an issue for potentially getting rid of this
dependency?
##########
arrow-cast/src/cast/run_array.rs:
##########
@@ -0,0 +1,262 @@
+use crate::cast::*;
+use arrow_ord::partition::partition;
+
+/// Attempts to cast a Run-End Encoded array to another type, handling both
REE-to-REE
+/// and REE-to-other type conversions with proper validation and error
handling.
+///
+/// # Arguments
+/// * `array` - The input Run-End Encoded array to be cast
+/// * `to_type` - The target data type for the casting operation
+/// * `cast_options` - Options controlling the casting behavior (e.g., safe vs
unsafe)
+///
+/// # Returns
+/// A `Result` containing the new `ArrayRef` or an `ArrowError` if casting
fails
+///
+/// # Behavior
+/// This function handles two main casting scenarios:
+///
+/// ## Case 1: REE-to-REE Casting
+/// When casting to another Run-End Encoded type:
+/// - Casts both the `values` and `run_ends` to their target types
+/// - Validates that run-end casting only allows upcasts (Int16→Int32,
Int16→Int64, Int32→Int64)
+/// - Preserves the REE structure while updating both fields
+/// - Returns a new `RunArray` with the appropriate run-end type (Int16,
Int32, or Int64)
+///
+/// ## Case 2: REE-to-Other Casting
+/// When casting to a non-REE type:
+/// - Expands the REE array to its logical form by unpacking all values
+/// - Applies the target type casting to the expanded array
+/// - Returns a regular array of the target type (e.g., StringArray,
Int64Array)
+///
+/// # Error Handling, error occurs if:
+/// - the input array is not a Run-End Encoded array
+/// - run-end downcasting would cause overflow
+/// - the target run-end type is unsupported
+/// - Propagates errors from underlying casting operations
+///
+/// # Safety Considerations
+/// - Run-end casting uses `safe: false` to prevent silent overflow
Review Comment:
Removed this comment
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