andygrove commented on a change in pull request #8024:
URL: https://github.com/apache/arrow/pull/8024#discussion_r475106389
##########
File path: rust/datafusion/src/execution/physical_plan/expressions.rs
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@@ -991,30 +991,236 @@ impl fmt::Display for BinaryExpr {
}
}
+// Returns a formatted error about being impossible to coerce types for the
binary operator.
+fn coercion_error<T>(lhs_type: &DataType, op: &String, rhs_type: &DataType) ->
Result<T> {
+ Err(ExecutionError::General(
+ format!(
+ "The binary operator '{}' can't evaluate with lhs = '{:?}' and rhs
= '{:?}'",
+ op, lhs_type, rhs_type
+ )
+ .to_string(),
+ ))
+}
+
+// the type that both lhs and rhs can be casted to for the purpose of a string
computation
+fn string_coercion(
+ lhs_type: &DataType,
+ op: &Operator,
+ rhs_type: &DataType,
+) -> Result<DataType> {
+ use arrow::datatypes::DataType::*;
+ match (lhs_type, rhs_type) {
+ (Utf8, Utf8) => Ok(Utf8),
+ (LargeUtf8, Utf8) => Ok(LargeUtf8),
+ (Utf8, LargeUtf8) => Ok(LargeUtf8),
+ (LargeUtf8, LargeUtf8) => Ok(LargeUtf8),
+ _ => coercion_error(lhs_type, &format!("{}", op), rhs_type),
+ }
+}
+
+/// coercion rule for numerical values
+pub fn numerical_coercion(
+ lhs_type: &DataType,
+ op: &String,
Review comment:
I'm curious why `string_coercion` takes `op` as `&Operator` but
`numerical_coercion` takes it as `&String`
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