timsaucer commented on code in PR #21030: URL: https://github.com/apache/datafusion/pull/21030#discussion_r3142056491
########## datafusion/ffi/README.md: ########## @@ -65,14 +65,39 @@ to work across Rust libraries. In general, you can use Rust's [FFI] to operate across different programming languages, but that is not the design intent of this crate. Instead, we are using external crates that provide stable interfaces that closely mirror the Rust native approach. To learn more -about this approach see the [abi_stable] and [async-ffi] crates. +about this approach see the [stabby] and [async-ffi] crates. If you have a library in another language that you wish to interface to DataFusion the recommendation is to create a Rust wrapper crate to interface with your library and then to connect it to DataFusion using this crate. Alternatively, you could use [bindgen] to interface directly to the [FFI] provided by this crate, but that is currently not supported. +## Stabby Usage + +This crate uses [stabby] for ABI-stable types like `stabby::string::String` and +`stabby::vec::Vec`. + +We intentionally use `#[repr(C)]` for our struct definitions instead of stabby's +`#[stabby::stabby]` macro for the following reasons: + +1. **Build time**: The heavy macro use greatly increases build time, especially + given our many interdependent types. + +2. **Code complexity**: Creating stabby dyn pointers for trait objects leads to + more complex code patterns with very little added benefit. + +3. **Arrow types**: Arrow's FFI types like `FFI_ArrowSchema` do not implement + `IStable`, and adding such implementations would be laborious and error-prone. + +4. **FFI_Option and FFIResult**: We provide our own `FFI_Option<T>` and + `FFIResult<T>` types using `#[repr(C, u8)]` because stabby's `Option` + and `Result` require inner types to be `IStable`. + +Instead, we use stabby for its convenient ABI-stable collection types like +`stabby::string::String` and `stabby::vec::Vec`, while retaining flexibility +for our complex FFI struct layouts. Review Comment: ```suggestion We use stabby for its convenient ABI-stable collection types like `stabby::string::String` and `stabby::vec::Vec`, while retaining flexibility for our complex FFI struct layouts. We provide our own `FFI_Option<T>` and `FFIResult<T>` types using `#[repr(C, u8)]` because stabby's `Option` and `Result` require inner types to be `IStable`. ``` -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
