Function erlang_nif_sys::erlang_nif_sys_api::enif_get_map_size

pub unsafe extern "C" fn enif_get_map_size(
    env: *mut ErlNifEnv, 
    term: ERL_NIF_TERM, 
    size: *mut size_t
) -> c_int

See enif_get_map_size in the Erlang docs.