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TS 游乐场示例

示例代码

type Base = {
  name: string
}

type ExtA = {
  address: string
}

type ExtB = {
  streetName: string;
}

function handler<T extends Base>(input: T): T {return input}
/** how do I build an object up? */


let payload = {
  name: "Aaron"
}
const addA = <T extends Base>(payload: T): T & ExtA => {
  return {
    ...payload,
    type: "a",
    address: "123 Fake St"
  }
}
const addB = <T extends Base>(payload: T): T & ExtB => {
  return {
    ...payload,
    type: "b",
    streetName: "Main"
  }
}

payload = addA(payload)
payload = addB(payload)

// type should be Base & ExtA & ExtB but it isn't
const wrongType = handler(payload)
//    ^?

我期望payload在通过操作函数时改变类型addA，addB但事实并非如此。如何让 TS 理解此变量的类型应该改变？