abi-vtable-macro

#[abi_vtable] — annotate a Rust trait and get the complete C contract for dyn-loader's abi mode: a #[repr(C)] vtable struct, one extern "C" thunk per method, a static vtable instance, a #[no_mangle] getter — and a host-side safe wrapper (CalcHost) with one safe method per trait method — all generated.

use abi_vtable_macro::abi_vtable;

#[abi_vtable(name = "calc")]
pub trait Calc {
    fn add(&self, a: i32, b: i32) -> i32;
    fn is_even(&self, x: i32) -> bool;
}

struct MyCalc;
impl Calc for MyCalc {
    fn add(&self, a: i32, b: i32) -> i32 { a + b }
    fn is_even(&self, x: i32) -> bool { x % 2 == 0 }
}

// One line: static instance + thunks + vtable + getter.
abi_vtable_impl_calc!(MyCalc, MyCalc);

The host (Rust, C, C++, Zig, ...) loads calc_get_vtable and calls through the struct of function pointers — see dyn-loader's AbiTable. A Rust host that declares the same trait with the same #[abi_vtable] attribute also gets the generated CalcHost wrapper and calls it safely:

let module = unsafe { AbiTable::<CalcVtable>::load(path, b"calc_get_vtable\0")? };
let host = CalcHost::new(module.vtable(), std::ptr::null_mut());
let sum = host.add(2, 3); // safe — no unsafe block needed

Rules

• Field order of the generated vtable is the protocol: it follows trait method declaration order. Never reorder after release.
• All fn pointers are extern "C" (cdecl), ctx-leading (*mut c_void first).
• $instance must be const-constructible (unit struct, const fn, literal).

License

MIT