# Required

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

我们发现一个有意思的用法 `-?`, 这里很好理解就是将可选项代表的 `?` 去掉, 从而让这个类型变成必选项. 与之对应的还有个`+?` , 这个含义自然与`-?`之前相反, 它是用来把属性变成可选项的.


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