// create a new empty arena
let mut arena = Arena::new();

// add values to it and store their returned IDs
let a = arena.insert('A');
let b = arena.insert('B');
let c = arena.insert('C');
let d = arena.insert('D');

// we can use those IDs to fetch the values
assert_eq!(arena.get(a), Some(&'A'));
assert_eq!(arena.get(b), Some(&'B'));
assert_eq!(arena.get(c), Some(&'C'));
assert_eq!(arena.get(d), Some(&'D'));

// the values live in a contiguous vector we can access
assert_eq!(arena.as_slice(), &['A', 'B', 'C', 'D']);

// we can remove a value from anywhere using its ID
arena.remove(b);

// the value at the end will fill the hole left by the removed one
assert_eq!(arena.as_slice(), &['A', 'D', 'C']);

// even though 'D' moved, its ID is still valid and can be used
assert_eq!(arena.get(a), Some(&'A'));
assert_eq!(arena.get(b), None);
assert_eq!(arena.get(c), Some(&'C'));
assert_eq!(arena.get(d), Some(&'D'));

// we can even sort the values to order them
arena.sort();

// and all the IDs will still be valid
assert_eq!(arena.as_slice(), &['A', 'C', 'D']);
assert_eq!(arena.get(a), Some(&'A'));
assert_eq!(arena.get(b), None);
assert_eq!(arena.get(c), Some(&'C'));
assert_eq!(arena.get(d), Some(&'D'));