js8544 opened a new pull request, #33608:
URL: https://github.com/apache/arrow/pull/33608
…t functions
# Which issue does this PR close?
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Closes #33607
# Rationale for this change
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Sometimes we need extra arguments for the `Visit` function, the most common
of which is output parameters to save the result. For now, we need to have a
member variable and a member function to get the result:
```cpp
class ExampleVisitor {
public:
template <typename T>
Status Visit(const T& arr) {
/// Do stuff and save result to output_;
return Status::OK();
}
std::shared_ptr<Array> GetOutput() { return output_; }
private:
std::shared_ptr<Array> output_;
};
ExampleVisitor visitor;
RETURN_NOT_OK(VisitArrayInline(*arr, &visitor));
*output = visitor.GetOutput();
```
It will be more convenient to write a Visitor if the VisitArrayInline
function supports additional args for the `Visit` method:
```cpp
class ExampleVisitorWithArg {
public:
template <typename T>
Status Visit(const T& arr, std::shared_ptr<Array>* output) {
/// Do stuff and save result to output directly;
return Status::OK();
}
};
ExampleVisitorWithArg visitor;
RETURN_NOT_OK(VisitArrayInline(*arr, &visitor, &output));
```
# Are these changes tested?
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Not sure if we need to explicitly test this feature, since no runtime
behavior is changed.
# Are there any user-facing changes?
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There is a small chance, like in diff.cc:402, `VisitTypeInline` is declared
as a friend function. The declaration needs to be changed.
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