``` function check(v: unknown): v is { name: string; age: number } { if (typeof v !== 'object' || v === null) { return false; } const a = v as { name: unknown; age: unknown }; if (typeof a.name !== 'string' || typeof a.age !== "number") { return false; } return true; } ```
其中 `const a = v as { name: unknown; age: unknown }` 比较丑, 怎么写才好?