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类型并没有被直接计算出来,可以使用 xxx extends any ? xx : never OR xxx extends never ? never : xxx #7

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xiaochengzi6 opened this issue Feb 23, 2023 · 0 comments

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xiaochengzi6 commented Feb 23, 2023

就比如这种

type DeepReadOnly<Obj extends Record<string, any>> = {
  readonly [Key in keyof Obj]: 
    Obj[Key] extends object
      ? Obj[Key] extends Function 
        ? Obj[Key]
        : DeepReadOnly<Obj[Key]>
      : Obj[Key]

}

type deepReadOnly = DeepReadOnly<{
  a: string
  b: number
  c: {
    d: number
    e: {
      name: string
    }
  }
}>

因为 ts 的类型只有被用到的时候才会做计算。

所以可以在前面加上一段 Obj extends never ? never 或者 Obj extends any 等，从而触发计算：

type DeepReadOnly<Obj extends Record<string, any>> = 
  Obj extends any ?
  {
    readonly [Key in keyof Obj]:
    Obj[Key] extends object
      ? Obj[Key] extends Function
        ? Obj[Key]
        : DeepReadOnly<Obj[Key]>
      : Obj[Key]
  }
  : never

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