扩展set的用法，使其具有多个索引

class MultiIndexSet {
  constructor() {
    this.map = new Map();
  }

  add(item) {
    const keys = this.getKeys(item);
    keys.forEach(key => {
      if (!this.map.has(key)) {
        this.map.set(key, new Set());
      }
      this.map.get(key).add(item);
    });
  }

  has(item) {
    const keys = this.getKeys(item);
    return keys.every(key => this.map.has(key) && this.map.get(key).has(item));
  }

  delete(item) {
    const keys = this.getKeys(item);
    let found = false;
    keys.forEach(key => {
      if (this.map.has(key)) {
        this.map.get(key).delete(item);
        found = true;
        if (this.map.get(key).size === 0) {
          this.map.delete(key);
        }
      }
    });
    return found;
  }

  getKeys(item) {
    // 假设每个对象都有'name'和'email'属性
    return [item.name, item.email];
  }

  getItems(key) {
    return this.map.get(key) || new Set();
  }
}

// 使用示例
const users = new MultiIndexSet();
users.add({ name: 'Alice', email: 'alice@example.com' });
users.add({ name: 'Bob', email: 'bob@example.com' });

console.log(users.has({ name: 'Alice', email: 'alice@example.com' })); // true
console.log(users.getItems('Alice')); // Set { { name: 'Alice', email: 'alice@example.com' } }