条件类型的打字稿枚举类型检查？

Question

我有 restful 服务接受枚举值作为数字或字符串，但总是 return 只是数字。有没有办法输入它们？

这是我想要的，但它在语法上无效：

enum Features {
  "A" = 1,
  "B" = 2,
  "C" = 2
}

type EnumOrString<T> = T extends enum
  ? T | keyof T
  : T

declare function getData(featureFilter: EnumOrString<Features>[]): Features[]

getData 采用枚举值数组或枚举键，但 return 仅采用枚举值。

I also would want to extend this to mapped types like DeepPartial 以便任何嵌套枚举都得到这种处理 - 无需具有由请求和响应划分的单独类型层次结构。

Answer 1

我认为 "identify an enum" 现在不可能。即使可以，您也无法以编程方式从 Features 类型（这是 Features 枚举的元素）转换为 typeof Features类型（从键到 Features 元素的映射）首先不知道 Features。同样：例如，类型 Features.B 对字符串文字 "B" 一无所知。只有 typeof Features 有一个属性像 {B: Features.B}。如果您希望类型函数从 Features 转换为 Features | keyof typeof Features，您需要明确提及 typeof Features。因此，即使您拥有梦想中的 extends enum 表示法，您仍然需要使用您关心的映射列表来编写替换代码。对不起。

仅解决递归部分，如果它很重要，这里是我如何递归处理一个类型以用枚举值和相关键：

enum Features {
  "A" = 1,
  "B" = 2,
  "C" = 2
}
type ValueOf<T> = T[keyof T]
type FeatureKey<T extends Features> =
  Extract<ValueOf<{
    [K in keyof typeof Features]: [K, typeof Features[K]]
  }>, [any, T]>[0]

type DeepFeaturesOrKey<T> =
  T extends Features ? (T | FeatureKey<T>) :
  T extends Array<infer L> ? DeepFeaturesOrKeyArray<L> :
  T extends object ? { [K in keyof T]: DeepFeaturesOrKey<T[K]> } : T

interface DeepFeaturesOrKeyArray<L> extends Array<DeepFeaturesOrKey<L>> { }

如果您没有指定整个事物（例如，您使用的是 discriminated union keyed off a specific enum value), and of course, the whole deep-whatever Array trickery to avoid the dreaded "circular reference" error message mentioned here:

，则棘手的位是提取枚举的子集

Similar to union and intersection types, conditional types are not permitted to reference themselves recursively (however, indirect references through interface types or object literal types are allowed)

我们来测试一下：

interface Foo {
  bar: string,
  baz: Features,
  qux: {
    a: Features[],
    b: boolean
  },
  quux: Features.A,
  quuux: Features.B  
}

type DeepFeaturesOrKeyFoo = DeepFeaturesOrKey<Foo>
declare const deepFeaturesOrKeyFoo: DeepFeaturesOrKeyFoo
deepFeaturesOrKeyFoo.bar; // string
deepFeaturesOrKeyFoo.baz; // Features | "A" | "B" | "C"
deepFeaturesOrKeyFoo.qux.a[1];  // Features | "A" | "B" | "C"
deepFeaturesOrKeyFoo.qux.b; // boolean
deepFeaturesOrKeyFoo.quux; // Features.A | "A"
deepFeaturesOrKeyFoo.quuux; // Features.B | "B" | "C" 
// note that the compiler considers Features.B and Features.C to be the
// same value, so this becomes Features.B | "B" | "C"

看起来不错。希望对您有所帮助。

条件类型的打字稿枚举类型检查？

Typescript enum type check for conditional types?

typescript

enums

mapped-types

conditional-types