litao3rd commented on issue #37840:
URL: https://github.com/apache/arrow/issues/37840#issuecomment-1734070333
> Oops, let me have a try with master, I've check some `CountRows` and
`Scan` code in master but at first glance they should works well.
>
> I've test that the result status of `Scan` is failed like above:
>
> ```
> Result<const Kernel*> CastFunction::DispatchExact(
> const std::vector<TypeHolder>& types) const {
> RETURN_NOT_OK(CheckArity(types.size()));
>
> std::vector<const ScalarKernel*> candidate_kernels;
> for (const auto& kernel : kernels_) {
> if (kernel.signature->MatchesInputs(types)) {
> candidate_kernels.push_back(&kernel);
> }
> }
>
> if (candidate_kernels.size() == 0) {
> return Status::NotImplemented("Unsupported cast from ",
types[0].type->ToString(),
> " to ", ToTypeName(out_type_id_), "
using function ",
> this->name());
> }
> ```
>
> Because field_type is null, and column is int64.
I am not very familier with C++ so that I cound not understand this code
snippet well. Could you kindly provide a complete snippet to illustrate how
this code works? This would greatly assist me in grasping its workings.
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