typescript
1class PostalCodeInfo {
2  constructor(
3    public readonly city: string,
4    public readonly state: string,
5    public readonly county: string,
6    public readonly timezone: string,
7    public readonly dstObserved: boolean
8  ) {
9    Object.freeze(this); // Ensure immutability
10  }
11}
12
13class PostalCodeFactory {
14  private cache = new Map<string, PostalCodeInfo>();
15  private stats = { hits: 0, misses: 0 };
16
17  get(postalCode: string): PostalCodeInfo {
18    if (this.cache.has(postalCode)) {
19      this.stats.hits++;
20      return this.cache.get(postalCode)!;
21    }
22
23    this.stats.misses++;
24    const info = this.lookup(postalCode);
25    this.cache.set(postalCode, info);
26    return info;
27  }
28
29  private lookup(postalCode: string): PostalCodeInfo {
30    // Simulated database/API lookup
31    return new PostalCodeInfo(
32      'City Name',
33      'ST',
34      'County Name',
35      'America/New_York',
36      true
37    );
38  }
39
40  getCacheStats() {
41    return { ...this.stats, size: this.cache.size };
42  }
43}