jayzhan211 commented on code in PR #14440:
URL: https://github.com/apache/datafusion/pull/14440#discussion_r1961634449
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datafusion/expr-common/src/signature.rs:
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@@ -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:
First of all, is there any function that need `AnyType` coercible to X?
Datafusion doesn't need this and neither do Spark function, they have their own
coercion rule, and coerce `AnyType` to X ends up incorrect coercion.
Second, if there is such use case, you can also implement it with
UserDefined signature.
If we have find a common used function that require `AnyType` to X then it
is a good reason to implement such functionality in coercion. We can add
another variant `Any`, it is not an issue.
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