Dandandan commented on a change in pull request #9376:
URL: https://github.com/apache/arrow/pull/9376#discussion_r571419483
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File path: rust/datafusion/src/physical_plan/string_expressions.rs
##########
@@ -17,27 +17,108 @@
//! String expressions
-use crate::error::{DataFusionError, Result};
-use arrow::array::{
- Array, ArrayRef, GenericStringArray, StringArray, StringBuilder,
- StringOffsetSizeTrait,
+use std::sync::Arc;
+
+use crate::{
+ error::{DataFusionError, Result},
+ scalar::ScalarValue,
+};
+use arrow::{
+ array::{Array, GenericStringArray, StringArray, StringOffsetSizeTrait},
+ datatypes::DataType,
};
-macro_rules! downcast_vec {
- ($ARGS:expr, $ARRAY_TYPE:ident) => {{
- $ARGS
- .iter()
- .map(|e| match e.as_any().downcast_ref::<$ARRAY_TYPE>() {
- Some(array) => Ok(array),
- _ => Err(DataFusionError::Internal("failed to
downcast".to_string())),
- })
- }};
+use super::ColumnarValue;
+
+/// applies a unary expression to `args[0]` that is expected to be
downcastable to
+/// a `GenericStringArray` and returns a `GenericStringArray` (which may have
a different offset)
+/// # Errors
+/// This function errors when:
+/// * the number of arguments is not 1
+/// * the first argument is not castable to a `GenericStringArray`
+pub(crate) fn unary_string_function<'a, T, O, F, R>(
+ args: &[&'a dyn Array],
+ op: F,
+ name: &str,
+) -> Result<GenericStringArray<O>>
+where
+ R: AsRef<str>,
+ O: StringOffsetSizeTrait,
+ T: StringOffsetSizeTrait,
+ F: Fn(&'a str) -> R,
+{
+ if args.len() != 1 {
+ return Err(DataFusionError::Internal(format!(
+ "{:?} args were supplied but {} takes exactly one argument",
+ args.len(),
+ name,
+ )));
+ }
+
+ let array = args[0]
+ .as_any()
+ .downcast_ref::<GenericStringArray<T>>()
+ .ok_or_else(|| {
+ DataFusionError::Internal("failed to downcast to
string".to_string())
+ })?;
+
+ // first map is the iterator, second is for the `Option<_>`
+ Ok(array.iter().map(|x| x.map(|x| op(x))).collect())
Review comment:
```suggestion
Ok(array.iter().map(|x| x.map(op).collect())
```
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