use crate::DataIndexable;
const PREVIOUS_DATA_INDEX_KEY: usize = 0;
pub trait PreviousDataIndex: DataIndexable {
fn get_previous_data_index(&self) -> Option<&usize> {
self.get_data_index(&PREVIOUS_DATA_INDEX_KEY, false)
}
fn set_previous_data_index(&mut self, index: usize) {
self.set_data_index(PREVIOUS_DATA_INDEX_KEY, index, false)
}
}