milenkovicm commented on issue #9529:
URL:
https://github.com/apache/arrow-datafusion/issues/9529#issuecomment-1988451635
```rust
// does not work
//
// the trait `ConfigExtension` cannot be made into an object
// `ConfigExtension` cannot be made into an object
// for a trait to be "object safe" it needs to allow building a vtable to
// allow the call to be resolvable dynamically; for more information visit
//
fn configuration(&self) -> Option<&dyn ConfigExtension> {
todo!()
}
```
```rust
//
// does work but I don't like it
//
// user can return whatever they want, registration process
// should try to register extension ...
// this would involve creating documentation to
// explain what we want, which makes bad API IMHO
fn configuration(&self) -> Option<dyn Any> {
None
}
```
```rust
// we can let user do it on init
// user should know what they are doing
//
// i dont find this api particullary useful at this point
fn init(&self, state: &mut SessionState) {
state.options().extensions.insert(extension)
}
```
```rust
/// config extension to register with this function factory
fn config_extension<T:ConfigExtension>() -> Option<T> where Self: Sized {
None
}
```
```rust
pub fn with_function_factory(
mut self,
function_factory: Arc<dyn FunctionFactory>,
) -> Self {
// the size for values of type `dyn FunctionFactory` cannot be known at
compilation time
// the trait `Sized` is not implemented for `dyn FunctionFactory
let c = <dyn FunctionFactory>::config_extension();
self.function_factory = Some(function_factory);
self
}
```
```rust
// it would force user to define `ConfigExtension`
pub fn with_function_factory<T: FunctionFactory + 'static, C :
ConfigExtension>(
mut self,
function_factory: Arc<T>,
) -> Self {
let c : Option<C> = T::config_extension();
self.function_factory = Some(function_factory);
self
}
```
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