Keep counts associated with unique keys.
const tally = new Tally<string>();tally.get('alice'); // 0tally.add('alice');tally.get('alice'); // 1tally.add('alice', 4);tally.get('alice'); // 5 Copy
const tally = new Tally<string>();tally.get('alice'); // 0tally.add('alice');tally.get('alice'); // 1tally.add('alice', 4);tally.get('alice'); // 5
Keep counts associated with unique keys.