use std::collections::hash_map::{self, HashMap};
#[cfg(feature = "unstable")]
use std::collections::hash_state::HashState;
-use std::default::Default;
use std::hash::Hash;
#[cfg(feature = "unstable")]
use std::hash::Hasher;
-use std::iter::IntoIterator;
#[cfg(feature = "unstable")]
use std::mem;
use std::ops::{Index, IndexMut};