alamb commented on issue #11513:
URL: https://github.com/apache/datafusion/issues/11513#issuecomment-2380710741
> I’d love to hear if this design is sound, or if there are any potential
pitfalls in how I’ve approached type mapping.
One thing I found a bit confusing was `ExtensionType::logical_type` in your
example returns a `LogicalType`
```rust
pub trait ExtensionType {
fn logical_type(&self) -> LogicalType;
}
```
But one of the `LogicalType` variants is itself an `ExtensionType`
```rust
#[derive(Clone)]
pub enum LogicalType {
//...
Extenstion(Arc<dyn ExtensionType>),
}
```
It seems like the idea is that the logical type would report its underlying
representation to DataFusion.
I wonder when we would ever need to know the "logical_type" of an extension
type. I think it would never make sense to DataFusion to treat a logical
extension type as its underlying representation
Just becase I know JSON columns are represented as Strings internally, I
think they should never be treated as Strings unless the user explicitly
requests such a conversion and the ExtensionType defines how to cast to a String
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