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Posted to github@arrow.apache.org by GitBox <gi...@apache.org> on 2022/06/26 17:36:54 UTC
[GitHub] [arrow-rs] jhorstmann opened a new issue, #1948: Reduce macro usage by abstracting over arrays that have a value or value_unchecked method
jhorstmann opened a new issue, #1948:
URL: https://github.com/apache/arrow-rs/issues/1948
**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**
Many Array types have a `value` and `value_unchecked` method. This method is not part of the `Array` trait because the return type would need to be a generic parameter, which would make the `Array` trait no longer object safe.
The absence of such a method makes it more difficult to abstract over different array types. For example the [iterators have a lot of code duplication](https://github.com/apache/arrow-rs/blob/9f7b6004d365b0c0bac8e30170b49bdd66cc7df0/arrow/src/array/iterator.rs#L135) or the [comparison functions use macros as a workaround](https://github.com/apache/arrow-rs/blob/9f7b6004d365b0c0bac8e30170b49bdd66cc7df0/arrow/src/compute/kernels/comparison.rs#L60).
**Describe the solution you'd like**
I propose to add another trait (maybe named `ArrayAccessor`) that would unify the types:
```rust
trait ArrayAccessor: Array {
type Item;
fn value(&self, index: usize) -> Self::Item;
unsafe fn value_unchecked(&self, index: usize) -> Self::Item;
}
```
This could be implemented by `PrimitiveArray`, `BooleanArray`, `StringArray`, `BinaryArray, `ListArray` and maybe more.
An interesting case is `DictionaryArray` where we might want two different accessors, one for keys and another that resolves keys to their corresponding values (haven't checked whether this would be possible to implement in a generic way).
Iterators and comparison kernels could then be implement in a generic way using this trait, reducing the amount of macros in the code base.
**Describe alternatives you've considered**
We could keep using macros.
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[GitHub] [arrow-rs] tustvold closed issue #1948: Reduce macro usage by abstracting over arrays that have a value or value_unchecked method
Posted by GitBox <gi...@apache.org>.
tustvold closed issue #1948: Reduce macro usage by abstracting over arrays that have a value or value_unchecked method
URL: https://github.com/apache/arrow-rs/issues/1948
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[GitHub] [arrow-rs] tustvold commented on issue #1948: Reduce macro usage by abstracting over arrays that have a value or value_unchecked method
Posted by GitBox <gi...@apache.org>.
tustvold commented on issue #1948:
URL: https://github.com/apache/arrow-rs/issues/1948#issuecomment-1229255111
The ArrayAccessor trait has been added and is slowly being integrated, I think this issue can now be closed as it isn't tracking anything specific
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[GitHub] [arrow-rs] martin-g commented on issue #1948: Reduce macro usage by abstracting over arrays that have a value or value_unchecked method
Posted by GitBox <gi...@apache.org>.
martin-g commented on issue #1948:
URL: https://github.com/apache/arrow-rs/issues/1948#issuecomment-1167394346
> ```rust
> fn value(&self, index: usize) -> Self::Item;
Shouldn't this return `Option<Self::Item>` ?
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[GitHub] [arrow-rs] tustvold commented on issue #1948: Reduce macro usage by abstracting over arrays that have a value or value_unchecked method
Posted by GitBox <gi...@apache.org>.
tustvold commented on issue #1948:
URL: https://github.com/apache/arrow-rs/issues/1948#issuecomment-1171264848
> as long as it is only used by methods that have an explicit where Self: Sized bound.
Unfortunately this would require you to specify the associated type as part of constructing the trait object, i.e. `Box<dyn Array<Item = Foo>>`.
That being said, having a separate `ArrayAccessor` trait makes a lot of sense to me
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[GitHub] [arrow-rs] jhorstmann commented on issue #1948: Reduce macro usage by abstracting over arrays that have a value or value_unchecked method
Posted by GitBox <gi...@apache.org>.
jhorstmann commented on issue #1948:
URL: https://github.com/apache/arrow-rs/issues/1948#issuecomment-1167372005
After reading https://doc.rust-lang.org/reference/items/traits.html#object-safety again this could also work as an associated type on `Array` itself, as long as it is only used by methods that have an explicit `where Self: Sized` bound.
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[GitHub] [arrow-rs] HaoYang670 commented on issue #1948: Reduce macro usage by abstracting over arrays that have a value or value_unchecked method
Posted by GitBox <gi...@apache.org>.
HaoYang670 commented on issue #1948:
URL: https://github.com/apache/arrow-rs/issues/1948#issuecomment-1167297153
Could we add an associated type for `trait Array` directly?
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