pub unsafe extern "C" fn readstat_insert_string_ref(
writer: *mut readstat_writer_t,
variable: *const readstat_variable_t,
ref_: *mut readstat_string_ref_t,
) -> readstat_error_tpub unsafe extern "C" fn readstat_insert_string_ref(
writer: *mut readstat_writer_t,
variable: *const readstat_variable_t,
ref_: *mut readstat_string_ref_t,
) -> readstat_error_t