zanmato1984 commented on code in PR #47297:
URL: https://github.com/apache/arrow/pull/47297#discussion_r2268383523
##########
cpp/src/arrow/compute/kernel.cc:
##########
@@ -475,23 +475,78 @@ std::string OutputType::ToString() const {
return "computed";
}
+// ----------------------------------------------------------------------
+// MatchConstraint
+
+std::shared_ptr<MatchConstraint> DecimalsHaveSameScale() {
+ class DecimalsHaveSameScaleConstraint : public MatchConstraint {
+ public:
+ bool Matches(const std::vector<TypeHolder>& types) const override {
+ DCHECK_GE(types.size(), 2);
+ DCHECK(std::all_of(types.begin(), types.end(),
+ [](const TypeHolder& type) { return
is_decimal(type.id()); }));
+ auto ty0 = checked_cast<const DecimalType*>(types[0].type);
+ DCHECK_NE(ty0, nullptr);
Review Comment:
> I thought that `checked_cast` never return `nullptr` because there are
`static_assert()`s before `dynamic_cast`:
>
>
https://github.com/apache/arrow/blob/db1a8a9bf42bec2b643fc19d8e174dd5166cd621/cpp/src/arrow/util/checked_cast.h#L29-L34
Sorry I'm not following. Those two `static_assert`s only assert the from and
to types are classes. There can be cases that both are classes but without
inheritance, that can still result in `nullptr`?
>
> BTW, there is
>
> ```c++
> DCHECK(std::all_of(types.begin(), types.end(),
> [](const TypeHolder& type) { return
is_decimal(type.id()); }));
> ```
>
> before this `checked_cast`. It seems that this `DCHECK()` will be failed
when `checked_cast` return `nullptr`.
This `is_decimal` merely checks the internal `type_id`. I'm not sure if we
can assume `ty.type_id == Type::DECIMAL` implies `typeof(ty) == class
DecimalType`.
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