scovich commented on issue #8794:
URL: https://github.com/apache/arrow-rs/issues/8794#issuecomment-3563886963
One idea that's been percolating:
We already have `Array::as_any()`, which cuts through all the layers of
wrapping and returns a reference to the underlying concrete array. What if we
introduced a similar `Array::as_arc()` method? It wouldn't be perfect, but in
case the user passed `&Arc<dyn Array>` or even `&Arc<Arc<dyn Array>>` -- which
_does_ happen! -- we could clone the arc instead of creating a new one. And
even if we do need to create a new one, at least it's centralized (and can use
the unsafe/unchecked Array -> ArrayData -> Array path) instead of scattering
that logic all through the code base.
<details>
The tricky part is figuring out how to handle the recursion nicely -- it
would be most convenient for the method to return `Option<Arc<dyn Array>>`, so
that nesting Just Works. But then the caller ends up with an Option they have
to unwrap.
Maybe we compromise by having both `as_arc` and `as_arc_opt`, where the
former is the convenience wrapper (provided method) and the latter does the
real work?
```rust
pub trait Array: Debug + Send + Sync {
...
fn as_arc_opt(&self) -> Option<ArrayRef> {
None // most impl Array know nothing about presence/absence of Arc
}
fn as_arc(&self) -> ArrayRef {
self.as_arc_opt().unwrap_or_else(|| make_array(array.to_data()))
}
...
}
impl<T: Array> Array for &T {
...
fn as_arc_opt(&self) -> Option<ArrayRef> {
T::as_arc_opt(self)
}
...
}
impl Array for Arc<dyn Array> {
...
fn as_arc_opt(&self) -> Option<ArrayRef> {
Some(self.clone())
}
...
}
```
</details>
relevant:
[cast_with_options](https://docs.rs/arrow-cast/57.0.0/src/arrow_cast/cast/mod.rs.html#747-756)
could benefit from such a capability.
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