typescript 合并枚举

Question

我正在尝试合并枚举映射，代码运行:

enum One {
    a = 'a',
}

enum Two {
    aa = 'aa',
}

enum Three {
    aaa = 'aaa',
}

type unit = One | Two | Three;

const twoFromOne: Map<Two, One> = new Map([[Two.aa, One.a]]);
const threeFromTwo: Map<Three, Two> = new Map([[Three.aaa, Two.aa]]);
const combined: Map<unit, unit> = new Map([
    ...twoFromOne,
    ...threeFromTwo,
]);

但是我得到一个 typescript 编译器错误:

const twoFromOne: Map<Two, One>
No overload matches this call.
  Overload 1 of 3, '(iterable: Iterable<readonly [Two, One]>): Map<Two, One>', gave the following error.
    Argument of type '([Two, One] | [Three, Two])[]' is not assignable to parameter of type 'Iterable<readonly [Two, One]>'.
      The types returned by '[Symbol.iterator]().next(...)' are incompatible between these types.
...

我不明白这个错误，它是说一张 map 被分配到另一张 map 而不是合并吗？

Link to TS playground

Answer 1

问题如下:

TypeScript 以某种方式仅根据您提供的第一个映射 (...twoFromOnw) 推断类型。您可以将 添加到 MapConstructor(右侧)，这样 TypeScript 就不会推断那是类型，评估者使用 Map :

const combined: Map<unit, unit> = new Map<unit, unit>([
    ...threeFromTwo,
    ...twoFromOne,
]);