class Service {
  private db: Db;
  private cache: Cache;
  constructor(db: Db, cache: Cache) { this.db = db; this.cache = cache; }
  save(k: string) { this.db.write(k); }
  load(k: string) { return this.db.read(k); }
  put(k: string) { this.cache.set(k); }
  evict(k: string) { this.cache.drop(k); }
}
