bjchambers commented on a change in pull request #651:
URL: https://github.com/apache/arrow-rs/pull/651#discussion_r686455865
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File path: arrow/src/compute/kernels/temporal.rs
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@@ -166,8 +168,62 @@ where
Ok(b.finish())
}
+/// Add the given `time_delta` to each time in the `date_time` array.
+///
+/// # Errors
+/// If the arrays of different lengths.
+pub fn add_time<DateTime, TimeDelta>(
+ date_time: &PrimitiveArray<DateTime>,
+ time_delta: &PrimitiveArray<TimeDelta>,
+) -> Result<PrimitiveArray<DateTime>>
+where
+ DateTime: ArrowTimestampType,
Review comment:
One potential issue there is that you can't necessarily add months to a
`Time32`, since the latter doesn't have a date component. It would be possible
to express that as a trait, but it would be more complex. For instance:
```
trait ArrowTimeDeltaType<T: ArrowTemporalType> {
fn add_time(temporal: T::Native, delta: Self::Native) -> T::Native;
}
impl ArrowTimeDeltaType<Date32> for IntervalYearMonthType {
...
}
...
```
Specifically, instead of having the trait allow adding the time delta to
*anything* that is a `DateTime`, it could have an additional parameter
indicating what it can be added to. This would require more implementation
blocks, would express what kinds of arithmetic were supported.
Eg., we could have `impl ArrowTimeDeltaType<Time32> for DurationSecondType {
... }` but we wouldn't have one for `IntervalYearMonthType`.
Does that level of encoding the supported operations in the trait make
sense? The alternative would be to have fewer limitations at the type level and
instead make it a runtime error to pass an invalid time type. In that world,
the delta could have two functions -- one for adding to a `DateTime` and one
for adding to a `Time`, and could choose to throw an exception if it wasn't
supported on `Time`.
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