const cache = new Cache<string>(3); // Note: They key has to be a string, value can be any type
cache.set('hello1', 'world1');
cache.set('hello2', 'world2');
cache.set('hello3', 'world3');
cache.get('hello1')

const cache = new Cache<string>(3); // cache size = 3
cache.set('hello1', 'world1');
cache.set('hello2', 'world2');
cache.set('hello3', 'world3');
cache.set('hello4', 'world4'); // `hello1`(oldest entry evicted)
cache.get('hello1'); // Will be `undefined` because cache size is three
cache.invalidateKey('hello2');
cache.get('hello2'); // undefined because invalidated