jayzhan211 commented on code in PR #14440:
URL: https://github.com/apache/datafusion/pull/14440#discussion_r1961784030
##########
datafusion/expr-common/src/signature.rs:
##########
@@ -466,6 +551,186 @@ fn get_data_types(native_type: &NativeType) ->
Vec<DataType> {
}
}
+/// Represents type coercion rules for function arguments, specifying both the
desired type
+/// and optional implicit coercion rules for source types.
+///
+/// # Examples
+///
+/// ```
+/// use datafusion_expr_common::signature::{Coercion, TypeSignatureClass};
+/// use datafusion_common::types::{NativeType, logical_binary, logical_string};
+///
+/// // Exact coercion that only accepts timestamp types
+/// let exact = Coercion::new_exact(TypeSignatureClass::Timestamp);
+///
+/// // Implicit coercion that accepts string types but can coerce from binary
types
+/// let implicit = Coercion::new_implicit(
+/// TypeSignatureClass::Native(logical_string()),
+/// vec![TypeSignatureClass::Native(logical_binary())],
+/// NativeType::String
+/// );
+/// ```
+///
+/// There are two variants:
+///
+/// * `Exact` - Only accepts arguments that exactly match the desired type
+/// * `Implicit` - Accepts the desired type and can coerce from specified
source types
+#[derive(Debug, Clone, Eq, PartialOrd)]
+pub enum Coercion {
+ /// Coercion that only accepts arguments exactly matching the desired type.
+ Exact {
+ /// The required type for the argument
+ desired_type: TypeSignatureClass,
+ },
+
+ /// Coercion that accepts the desired type and can implicitly coerce from
other types.
+ Implicit {
+ /// The primary desired type for the argument
+ desired_type: TypeSignatureClass,
+ /// Rules for implicit coercion from other types
+ implicit_coercion: ImplicitCoercion,
+ },
Review Comment:
https://github.com/apache/datafusion/issues/14296
If we begin allowing user-defined coercion rules for other operations, not
just functions, users would need to define coercion rules for operations like
binary comparisons as well. In other hand, what you are suggesting could limit
the extensibility of coercion rules within DataFusion.
However, while we aim to provide extensibility, basic rules—such as
converting an integer to a broader integer type—can be implemented as default
rules in DataFusion, as long as they align well with the internal logic of the
system.
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