Github user chenghao-intel commented on a diff in the pull request: https://github.com/apache/spark/pull/7151#discussion_r33685497 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala --- @@ -266,16 +266,37 @@ abstract class UnaryExpression extends Expression with trees.UnaryNode[Expressio } /** + * An trait that gets mixin to define the expected input types of an expression. + */ +trait ExpectsInputTypes { self: Expression => + + /** + * Expected input types from child expressions. The i-th position in the returned seq indicates + * the type requirement for the i-th child. + * + * The possible values at each position are: + * 1. a specific data type, e.g. LongType, StringType. + * 2. a non-leaf data type, e.g. NumericType, IntegralType, FractionalType. + * 3. a list of specific data types, e.g. Seq(StringType, BinaryType). + */ + def inputTypes: Seq[Any] + + override def checkInputDataTypes(): TypeCheckResult = { + // We will do the type checking in `HiveTypeCoercion`, so always returning success here. + TypeCheckResult.TypeCheckSuccess + } +} + +/** * Expressions that require a specific `DataType` as input should implement this trait * so that the proper type conversions can be performed in the analyzer. */ -trait AutoCastInputTypes { - self: Expression => +trait AutoCastInputTypes { self: Expression => - def expectedChildTypes: Seq[DataType] + def inputTypes: Seq[DataType] override def checkInputDataTypes(): TypeCheckResult = { --- End diff -- Leave it unimplemented or throws exception, to force the expression developer think about what data types can be acceptable.
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