通用类型：动态类型检查特定对象属性：在通用类型 B 中使用类型 A 中的键~值对

Question

我目前有一个类型 (FieldTypeProperties)，我想在它的键传递给函数或对象时强制执行动态类型检查：

export enum supportedFields{
    Text = "Text",
    Note = "Note",
    Number = "Number"
}

export type FieldTypeProperties = {
    [supportedFields.Text]: TypeA;
    [supportedFields.Note]: TypeB;
    [supportedFields.Number]: TypeC;
};

我已经成功地定义了一个按预期运行的函数：

const createField = <K extends keyof FieldTypeProperties>(fieldType: K, properties: FieldTypeProperties[K]): IResult => {

  let field: IResult;

  //Some code

  return field;

}

用法按预期工作，fieldType 参数值确实检查属性参数中的正确类型：

let test = createField(supportedFields.Note, {});
// Checks for Type B in the properties argument, as defined in the FieldTypeProperties type

但是对于批处理操作，我想循环一个符合 createField() 参数的对象数组，所以：

type BatchObj<K extends keyof FieldTypeProperties> = {
    fieldType: K;
    properties: FieldTypeProperties[K];
}

// Intended Usage:
let testBatch1: BatchObj<keyof FieldTypeProperties>[] = [
  {
    fieldType: supportedFields.Text,
    properties: {}, //Type A should only be checked, but it's not, instead a union of TypeA | TypeB | TypeC is checked
  },
]

// Usage that works but is NOT desired:
let testBatch2: BatchObj<supportedFields.Text>[] = [
  {
    fieldType: supportedFields.Text,
    properties: {}, //Type A is checked, but now any additional objects added to this array must have a fieldType = supportedFields.Text and properties = TypeA
  }
]

我能理解为什么会这样，因为在 testBatch1 中： fieldType (K) 将是 FieldTypeProperties 类型的键集，属性 (FieldTypeProperties[K]) 将是集值FieldTypeProperties 类型。

根据上面代码片段中的推断，有没有办法实现我想要的用法？或者这是打字稿的限制，就目前而言是不可能的？

非常感谢您的回复:)

Answer 1

您可以为每个可能的键生成联合：BatchObj<"Text"> | BatchObj<"Note"> | BatchObj<"Number"> 使用条件类型的分布。这将确保 fieldType 和 properties 之间的关系得以保留：

type BatchObj<K extends keyof FieldTypeProperties> = {
    fieldType: K;
    properties: FieldTypeProperties[K];
}
type BatchObjUnion<K extends keyof FieldTypeProperties = keyof FieldTypeProperties>  = K extends K ? BatchObj<K>: never

// Intended Usage:
let testBatch1: BatchObjUnion[] = [
  {
    fieldType: supportedFields.Text,
    properties: { text: "" }, //Type A
  },
]

Playground Link

通用类型：动态类型检查特定对象属性：在通用类型 B 中使用类型 A 中的键~值对

Generic Types: Dynamically type check specific object properties: using key ~ value pair from Type A, in Generic Type B

typescript

typescript-generics