Typescript如何检查具有多种类型的对象的类型

type Student = {
  name: string;
  age: number;
  grade: string;
};

type Teacher = {
  name: string;
  age: number;
  subject: string;
};

type Person = Student | Teacher;

function printDetails(person: Person) {
  console.log(person.name);
  console.log(person.age);
  
  // 使用类型断言来判断具体类型并执行相应的操作
  if ('grade' in person) {
    console.log(person.grade);
  } else {
    console.log(person.subject);
  }
}

const student: Student = {
  name: 'Alice',
  age: 18,
  grade: 'A'
};

const teacher: Teacher = {
  name: 'Bob',
  age: 30,
  subject: 'Math'
};

printDetails(student); // 输出：Alice 18 A
printDetails(teacher); // 输出：Bob 30 Math