I’m having some trouble just returning ok from rust. The following fails with an Erlang error: :invalid_struct:

mod atoms {
    rustler::atoms! {
        ok
    }
}

#[rustler::nif]
pub fn backend_deallocate(array: ExAf) -> Atom {
    let exaf_array = array.resource.value();

    match exaf_array {
        ExAfArray::U8(a) => drop(a),
        ExAfArray::U16(a) => drop(a),
        ExAfArray::U32(a) => drop(a),
        ExAfArray::U64(a) => drop(a),
        ExAfArray::S16(a) => drop(a),
        ExAfArray::S32(a) => drop(a),
        ExAfArray::S64(a) => drop(a),
        ExAfArray::F16(a) => drop(a),
        ExAfArray::F32(a) => drop(a),
        ExAfArray::F64(a) => drop(a),
        ExAfArray::C64(a) => drop(a),
        ExAfArray::C128(a) => drop(a),
    }

    atoms::ok()
}

How can I return :ok (or any other atom) from Rust?