https://www.ithome.me/tags/%E7%B1%BB%E5%9E%8B%E7%B3%BB%E7%BB%9F/ Recent content in 类型系统 on 编程心语 Hugo zh-CN Tue, 04 Aug 2026 14:59:27 +0800 https://www.ithome.me/post/2026/07/09/type-driven-design-illegal-states/ Thu, 09 Jul 2026 08:00:00 +0800 https://www.ithome.me/post/2026/07/09/type-driven-design-illegal-states/ <h2 id="从一个-bug-说起">从一个 Bug 说起</h2> <p>你一定见过这样的代码：</p> <div class="highlight"><div class="chroma"> <table class="lntable"><tr><td class="lntd"> <pre tabindex="0" class="chroma"><code><span class="lnt">1 </span><span class="lnt">2 </span><span class="lnt">3 </span><span class="lnt">4 </span><span class="lnt">5 </span></code></pre></td> <td class="lntd"> <pre tabindex="0" class="chroma"><code class="language-typescript" data-lang="typescript"><span class="line"><span class="cl"><span class="kr">interface</span> <span class="nx">User</span> <span class="p">{</span> </span></span><span class="line"><span class="cl"> <span class="nx">id</span>: <span class="kt">string</span> </span></span><span class="line"><span class="cl"> <span class="nx">email</span>: <span class="kt">string</span> <span class="o">|</span> <span class="kc">null</span> </span></span><span class="line"><span class="cl"> <span class="nx">verified</span>: <span class="kt">boolean</span> </span></span><span class="line"><span class="cl"><span class="p">}</span> </span></span></code></pre></td></tr></table> </div> </div><p>看似合理，但仔细想想——一个 <code>email</code> 为 <code>null</code> 的用户，<code>verified</code> 能是 <code>true</code> 吗？显然不能。但在当前类型定义下，<code>{ email: null, verified: true }</code> 是完全合法的值。这就是<strong>非法状态可以表达</strong>的典型问题：类型系统允许存在逻辑上不可能的数据组合。</p>