ZhangHuiGui commented on code in PR #41012:
URL: https://github.com/apache/arrow/pull/41012#discussion_r1628675148
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cpp/src/arrow/compute/kernel.h:
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@@ -109,6 +109,9 @@ struct ARROW_EXPORT TypeMatcher {
/// \brief Return true if this matcher accepts the data type.
virtual bool Matches(const DataType& type) const = 0;
+ /// \brief Return true if this matcher accepts the combination types
+ virtual bool Matches(const std::vector<TypeHolder>& types) const { return
true; }
+
Review Comment:
Ah, the root cause of the problem that this PR is trying to solve is
actually CompareFunction with two different decimal scales in BindNonRecursive
, it is impossible to enter the logic of `DispatchBest`.
https://github.com/apache/arrow/blob/9ee6ea701e20d1b47934f977d87811624061d597/cpp/src/arrow/compute/expression.cc#L556-L563
Which means the `DispatchExact ` will always return ok and can't go into
`DispatchBest` when `CompareFunction` called by expression system with two
different decimal scales.
This is why we did type judgment in the output type Resolver before, so that
we can return not-ok in the first `FinishBind` and enter `DispatchBest`.
`DispatchBest` does not need to make additional judgments, because it will
do cast according to the decimal rules, ensuring that different input scales
are cast to the same scales according to `DecimalPromotion::kAdd`.
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