如何将数字枚举用作类型注释中的索引

Question

我想使用数字枚举作为对象的索引类型。

enum Weekday {
    Monday = 0,
    Tuesday = 1,
    Wednesday = 2,
    Thursday = 3,
    Friday = 4,
    Saturday = 5,
    Sunday = 6
};
const isWeekend: { [day: Weekday]: boolean } = {
    [Weekday.Monday]: false,
    [Weekday.Tuesday]: false,
    [Weekday.Wednesday]: false,
    [Weekday.Thursday]: false,
    [Weekday.Friday]: false,
    [Weekday.Saturday]: true,
    [Weekday.Sunday]: true,
};

此代码未通过类型检查，并显示以下消息：

索引签名参数类型必须是"字符串"或"数字"。

我知道几种解决方法。如果我将isWeekend的类型更改为{ [day: number]: boolean }它将编译，但类型会失去一些精度。

如何在不更改Weekday定义的情况下为isWeekend提供更精确的类型？

Answer 1

我只是自己解决了这个问题。我应该使用day in Weekday而不是day: Weekday.以下代码有效：

enum Weekday {
    Monday = 0,
    Tuesday = 1,
    Wednesday = 2,
    Thursday = 3,
    Friday = 4,
    Saturday = 5,
    Sunday = 6
};
const isWeekend: { [day in Weekday]: boolean } = {
    [Weekday.Monday]: false,
    [Weekday.Tuesday]: false,
    [Weekday.Wednesday]: false,
    [Weekday.Thursday]: false,
    [Weekday.Friday]: false,
    [Weekday.Saturday]: true,
    [Weekday.Sunday]: true,
};