alamb edited a comment on issue #1128:
URL: https://github.com/apache/arrow-rs/issues/1128#issuecomment-1005615737
I was able to use the borrow idea like this, but it still requires two
generic arguments to `as_primitive_array` (and thus requires many code level
changes which I am trying to avoid as then all existing callsites need to be
changed)
```rust
/// Force downcast ArrayRef to PrimitiveArray<T>
pub fn as_primitive_array<F, T>(arr: &F) -> &PrimitiveArray<T>
where
F: Borrow<dyn Array> + ?Sized,
T: ArrowPrimitiveType,
{
arr.borrow()
.as_any()
.downcast_ref::<PrimitiveArray<T>>()
.expect("Unable to downcast to primitive array")
}
```
I also tried using an `impl`
```rust
/// Force downcast ArrayRef to PrimitiveArray<T>
pub fn as_primitive_array<T>(arr: &(impl Borrow<dyn Array> + ?Sized)) ->
&PrimitiveArray<T>
where
T: ArrowPrimitiveType,
{
arr.borrow()
.as_any()
.downcast_ref::<PrimitiveArray<T>>()
.expect("Unable to downcast to primitive array")
}
```
which seemed to get me what I wanted, but then rust seemed to be unhappy
about mixing explicit and implicit generics:
```
error[E0632]: cannot provide explicit generic arguments when `impl Trait` is
used in argument position
--> arrow/src/compute/kernels/comparison.rs:904:49
|
904 | let left = as_primitive_array::<Int8Type>($LEFT);
| ^^^^^^^^ explicit
generic argument not allowed
...
1103 | | DataType::UInt64 => {dyn_compare_scalar!(&left, right,
key_type, eq_scalar)}
|
------------------------------------------------------ in this macro invocation
```
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