paleolimbot commented on PR #20312:
URL: https://github.com/apache/datafusion/pull/20312#issuecomment-4084643547
> Do you already have a design in your mind? If not, I can familiarize
myself with the casting system and try to come up with something.
I will give this a go tonight or tomorrow...I spent some time going through
the cast system last week. I was thinking something like:
```rust
pub trait DFExtensionType: Debug + Send + Sync {
// ...
fn create_cast_extension(&self) -> Option<Box<dyn CastExtension>> { None
}
}
pub trait CastExtension {
fn can_cast(&self, to: &Field, <options, or at least bool implicit>) ->
bool;
fn can_cast_from(&self, to: &Field, <options, or at least bool implicit>)
-> bool;
fn cast(&self, value: ColumnarValue, to: &Field) -> Result<ArrayRef>;
fn cast_from(&self, value: ColumnarValue, to: &Field) -> Result<ArrayRef>;
}
```
...which might need some workshopping to plug in to operator planning (e.g.,
common castable type, implicit vs. explicit casts). Another approach would be
to register a `CastExtension` with both types (to/from)...happy to experiment.
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