alamb commented on code in PR #6503:
URL: https://github.com/apache/arrow-datafusion/pull/6503#discussion_r1212296445
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datafusion/physical-expr/src/aggregate/first_last.rs:
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@@ -112,25 +112,35 @@ impl PartialEq<dyn Any> for FirstValue {
#[derive(Debug)]
struct FirstValueAccumulator {
first: ScalarValue,
+ // At the beginning, `is_set` is `false`, this means `first` is not seen
yet.
+ // Once we see (`is_set=true`) first value, we do not update `first`.
+ is_set: bool,
Review Comment:
Another potential way that might let the compiler check that `is_set` was
updated correctly would be something like:
```
struct FirstValueAccumulator {
/// None until the data has been seen
first: Option<ScalarValue>
}
```
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