so unsafe

terror.rust

#[no_mangle]
pub extern "C" fn wrenSetSlotNewForeign(
    vm: *mut WrenVM,
    slot: c_int,
    class_slot: c_int,
    size: size_t,
) -> *mut c_void {
    let mut user_data = UserDataWrapper {
        buffer: vec![0; size].into_boxed_slice(),
    };
    let c_ptr = user_data.buffer.as_mut_ptr();

    unsafe { std::mem::transmute::<*mut WrenVM, &mut RustWrenVM>(vm) }.set_slot_new_foreign(
        usize::try_from(slot).unwrap(),
        usize::try_from(class_slot).unwrap(),
        Box::new(user_data),
    );
    unsafe { std::mem::transmute::<*mut u8, *mut c_void>(c_ptr) }
}