felipecrv commented on code in PR #41012:
URL: https://github.com/apache/arrow/pull/41012#discussion_r1628457872
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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:
This class is for matching a single matcher (`this`) against a single type.
I don't think it's reasonable to extend the type matching this way as it
makes type checking Turing-complete (wouldn't be easy/possible to encode the
typing rules in a provably-decidable type system).
I'm sorry for this back and forth because I was the one that said "type
matching machinery". I still think this logic shouldn't go on the output type
resolver so I have a more precise suggestion this time. Since functions already
have a way of implementing custom type matching rules -- `DispatchBest` —— you
can add this logic in
https://github.com/apache/arrow/blob/9ee6ea701e20d1b47934f977d87811624061d597/cpp/src/arrow/compute/kernels/scalar_compare.cc#L343-L345
and return `return arrow::compute::detail::NoMatchingKernel(this, *types);`
or a `Status::NotImplemented` with a message that describes that you can't
compare two decimals with different scales.
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