Entrypoint — Loadable Extensions - Better DuckDB

Requires better-duck-core’s loadable-extension FFI mode (which implies udf). In that mode the crate links no DuckDB of its own and routes every FFI call through the host’s dynamically-loaded API table, building a cdylib. Re-exported as better_duck_core::duckdb_entrypoint.

#[duckdb_entrypoint] generates the C-ABI entrypoint DuckDB’s loader calls for a Rust-authored loadable extension (.duckdb_extension), wrapping a fn(&mut Connection) -> Result<…>.

use better_duck_core::{connection::Connection, duckdb_entrypoint, duckdb_scalar};

#[duckdb_scalar(name = "hello")]
fn hello(name: &str) -> String { format!("hello, {name}!") }

#[duckdb_entrypoint(name = "my_ext", min_duckdb_version = "v1.5.5")]
fn init(conn: &mut Connection) -> better_duck_core::error::Result<()> {
    hello::register(conn)?;        // register your UDFs on the host's connection
    Ok(())
}

The macro emits an exported my_ext_init_c_api symbol: it initializes the dynamically-loaded API table, obtains the host database, wraps it in a Connection via open_from_raw (which never closes the host-owned database), and invokes your init with &mut conn. An Err is reported back to DuckDB through the loader’s set_error.

Options

Option	Meaning
`name = "<extension>"`	Required. The extension name, driving the generated `<name>_init_c_api` symbol.
`min_duckdb_version = "v…"`	Minimum DuckDB C-API version to negotiate. Optional; defaults to `"v0.0.1"` (widest support).

The generated code depends on the loadable-extension feature’s API-table initializer (better_duck_core::extension_api::c_api_init) and Connection::open_from_raw. Until built in that mode, code produced by this macro will not compile — the macro itself is stable groundwork.

See also

Extensions — the loadable-extension feature and runtime extension management.
UDF overview — the functions you register inside init.
Opening connections — open_from_raw.