findepi commented on code in PR #14513:
URL: https://github.com/apache/datafusion/pull/14513#discussion_r1943188641
##########
datafusion/functions/src/utils.rs:
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@@ -18,10 +18,50 @@
use arrow::array::ArrayRef;
use arrow::datatypes::DataType;
-use datafusion_common::{Result, ScalarValue};
+use datafusion_common::{exec_datafusion_err, Result, ScalarValue};
use datafusion_expr::function::Hint;
use datafusion_expr::ColumnarValue;
+/// Converts a collection of function arguments into an fixed-size array of
length N
+/// producing a reasonable error message in case of unexpected number of
arguments.
+///
+/// # Example
+/// ```
+/// # use datafusion_common::ScalarValue;
+/// # use datafusion_common::Result;
+/// # use datafusion_expr_common::columnar_value::ColumnarValue;
+/// fn my_function(args: &[ColumnarValue]) -> Result<()> {
+/// // function expects 2 args, so create a 2-element array
+/// let [arg1, arg2] = take_function_args("my_function", args)?;
+/// // ... do stuff..
+/// Ok(())
+/// }
+///
+/// // Calling the function with 1 argument produces an error:
+/// let ten = ColumnarValue::from(ScalarValue::from(10i32));
+/// let twenty = ColumnarValue::from(ScalarValue::from(20i32));
+/// let args = vec![ten.clone()];
+/// let err = my_function(&args).unwrap_err();
+/// assert_eq!(err.to_string(), "my_function function requires 2 arguments,
got 1");
+/// // Calling the function with 2 arguments works great
+/// let args = vec![ten, twenty];
+/// my_function(&args).unwrap();
+/// ```
+pub fn take_function_args<const N: usize, T>(
+ function_name: &str,
+ args: impl IntoIterator<Item = T>,
+) -> Result<[T; N]> {
+ let args = args.into_iter().collect::<Vec<_>>();
+ args.try_into().map_err(|v: Vec<T>| {
+ exec_datafusion_err!(
+ "{} function requires {} arguments, got {}",
+ function_name,
+ N,
Review Comment:
BTW generally the error messages should start with a constant prefix string,
with variable part pushed as late as possible. for example "Invalid argument
count for function {}: expected {}, got {}".
this makes them more findable in the code.
i didn't do this in this PR to maintain compat with existing tests asserting
a particular error string
to be revisited in the future
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