jayzhan211 commented on code in PR #9610:
URL: https://github.com/apache/arrow-datafusion/pull/9610#discussion_r1528423492
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datafusion/functions/src/core/arrow_cast.rs:
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@@ -15,63 +15,123 @@
// specific language governing permissions and limitations
// under the License.
-//! Implementation of the `arrow_cast` function that allows
-//! casting to arbitrary arrow types (rather than SQL types)
+//! [`ArrowCastFunc`]: Implementation of the `arrow_cast`
+use std::any::Any;
use std::{fmt::Display, iter::Peekable, str::Chars, sync::Arc};
use arrow_schema::{DataType, Field, IntervalUnit, TimeUnit};
use datafusion_common::{
- plan_datafusion_err, DFSchema, DataFusionError, Result, ScalarValue,
+ internal_err, plan_datafusion_err, plan_err, DataFusionError, ExprSchema,
Result,
+ ScalarValue,
};
-use datafusion_common::plan_err;
-use datafusion_expr::{Expr, ExprSchemable};
+use datafusion_expr::simplify::{ExprSimplifyResult, SimplifyInfo};
+use datafusion_expr::{ColumnarValue, Expr, ScalarUDFImpl, Signature,
Volatility};
-pub const ARROW_CAST_NAME: &str = "arrow_cast";
-
-/// Create an [`Expr`] that evaluates the `arrow_cast` function
+/// Implements casting to arbitrary arrow types (rather than SQL types)
+///
+/// Note that the `arrow_cast` function is somewhat special in that its
+/// return depends only on the *value* of its second argument (not its type)
///
-/// This function is not a [`BuiltinScalarFunction`] because the
-/// return type of [`BuiltinScalarFunction`] depends only on the
-/// *types* of the arguments. However, the type of `arrow_type` depends on
-/// the *value* of its second argument.
+/// It is implemented by calling the same underlying arrow `cast` kernel as
+/// normal SQL casts.
///
-/// Use the `cast` function to cast to SQL type (which is then mapped
-/// to the corresponding arrow type). For example to cast to `int`
-/// (which is then mapped to the arrow type `Int32`)
+/// For example to cast to `int` using SQL (which is then mapped to the arrow
+/// type `Int32`)
///
/// ```sql
/// select cast(column_x as int) ...
/// ```
///
-/// Use the `arrow_cast` functiont to cast to a specfic arrow type
+/// You can use the `arrow_cast` functiont to cast to a specific arrow type
///
/// For example
/// ```sql
/// select arrow_cast(column_x, 'Float64')
/// ```
-/// [`BuiltinScalarFunction`]: datafusion_expr::BuiltinScalarFunction
-pub fn create_arrow_cast(mut args: Vec<Expr>, schema: &DFSchema) ->
Result<Expr> {
+#[derive(Debug)]
+pub(super) struct ArrowCastFunc {
+ signature: Signature,
+}
+
+impl ArrowCastFunc {
+ pub fn new() -> Self {
+ Self {
+ signature: Signature::any(2, Volatility::Immutable),
+ }
+ }
+}
+
+impl ScalarUDFImpl for ArrowCastFunc {
+ fn as_any(&self) -> &dyn Any {
+ self
+ }
+
+ fn name(&self) -> &str {
+ "arrow_cast"
+ }
+
+ fn signature(&self) -> &Signature {
+ &self.signature
+ }
+
+ fn return_type(&self, arg_types: &[DataType]) -> Result<DataType> {
+ parse_data_type(&arg_types[1].to_string())
Review Comment:
If `return_type_from_exprs` exists, we don't need `return_type`
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