[GitHub] [arrow] Light-City commented on issue #35863: [C++] Can InputType support nested types in the future?

["Light-City (via GitHub)" <gi...@apache.org>]

Light-City commented on issue #35863:
URL: https://github.com/apache/arrow/issues/35863#issuecomment-1585945204

   > I'm not sure I understand your goal. Is it to only need a single custom type matcher? Would it be possible to do:
   > 
   > ```
   > class AvgFinalMatcher : public TypeMatcher {
   >  public:
   >   AvgFinalMatcher(Type::type type_id) : type_id_(type_id) {}
   > 
   >   bool Matches(const DataType& type) const override {
   >     if (type.id() != Type::STRUCT) {
   >       return false;
   >     }
   >     return (type.fields()[0])->type()->id() == type_id_;
   >   }
   > private:
   >   Type::type type_id_;
   >  //......
   > }
   > 
   > // ...
   > 
   > Status Visit(const Decimal128Type&) {
   >     kernel = MakeKernel(std::move(InputType(match::AvgFinal(Type::DECIMAL128), ValueDescr::ARRAY)),
   >                         AvgSumInit<GroupedAvgFinalImpl<Decimal128Type>>);
   >     return Status::OK();
   >   }
   > 
   >   Status Visit(const Decimal256Type&) {
   >     kernel = MakeKernel(std::move(InputType(match::AvgFinal(Type::DECIMAL256), ValueDescr::ARRAY)),
   >                         AvgSumInit<GroupedAvgFinalImpl<Decimal256Type>>);
   >     return Status::OK();
   >   }
   > ```
   
   yes, We don't know the specific internal type, it needs to be determined according to the input, that is, this Matches lacks a parameter(just for inputType)


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