减法运算符和in关键字在typescript Required<T>实现中的应用

let result = 10 - 5;
console.log(result); // 输出 5

interface Person {
  name: string;
  age?: number;
}

function printPerson(person: Person) {
  if ('age' in person) {
    console.log(person.age);
  } else {
    console.log('age属性不存在');
  }
}

let person1: Person = { name: 'Alice' };
let person2: Person = { name: 'Bob', age: 20 };

printPerson(person1); // 输出 "age属性不存在"
printPerson(person2); // 输出 20

type Required<T> = {
  [P in keyof T]-?: T[P];
};

interface Person {
  name: string;
  age?: number;
}

type RequiredPerson = Required<Person>;

let person: RequiredPerson = { name: 'Alice', age: 20 };
console.log(person.age); // 输出 20