Theo's Typesafe Cult•9mo ago

Type A is not assignable to type A & B & C. Not sure why ts infers with an `&` and not `|`

Unsure why this is happening. I am trying to create a function that can have multiple types and when a different function with a generic passing that argument it should infer it. Example below its a bit easier to understand in code that description. https://www.typescriptlang.org/play?#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-mF1jcfiRa5PEv91B2xSCPg6QyJ33+bTh5Ix3fe5PxLOzxio8vv8k-C3asdyA-dMDrI98BPVxvwXS9O1vHtWX7Qdhx0V8kOwSctClOdW2jWpZFkeNE01AhAwgAAxeEWkQAAeAAVBYdmWQFMgsPlb3dQkKBQvcoFJDUoGCcde3wJiXBo1NfXIU1ahIpN+ggHDEEQ+9xL48FqxEt9WV4UTWUIthtATJMU0pI9eBecQACtlOASdhQIGlzIIblJxk4YaRpSE+MhKAADIAqgEwIAoMI+jAHz3MGIguPlbleRoUZhSZX09XkNLkyZVNRkk4YIE800ZTlGiCC9aBnXlEAsE1LQaDITVyF9K49XlTACHk0zNWCczeFcyyguy3K6gGmEOmMjBMF9GkdMwwLgt6nKIF5LSMQUnr4N4JbUzqHcOkneDRiGnaID2isDqO2aDIfIzmCAA

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1 Reply

Alky•9mo ago

To be honest, i don't know exactly what you're trying to do, but i made what i think you want to do. See:

type ApiResponse<T extends string> = {
  [key in T]: string
} & {
  [key: string]: string
}

type APIERRORCODES3<T extends string> =
  | {
      [key: string]: {
        [key: number]: {
          i18nKey: T
          values?: (payload: ApiResponse<T>) => { [key in T]: string }
        }
      }
    }
  | {
      [key: string]: string
    }

const someFun2 = <T extends string>(path: string) => {
  let _payload: ApiResponse<T> | undefined
  const codes2: APIERRORCODES3<T> = {}

  const codesKey = Object.keys(codes2).find((k) => RegExp(k).test(path)) as keyof APIERRORCODES3<T> | undefined // unsure why it cant infer this

  const _code = codesKey && codes2[codesKey]

  if (_payload && _code && typeof _code === 'object') {
    const _value = _code[100].values && _code[100].values(_payload)
    return _value
  } else {
    return undefined
  }
}

const test = someFun2<'A'>('/A')

type ApiResponse<T extends string> = {
  [key in T]: string
} & {
  [key: string]: string
}

type APIERRORCODES3<T extends string> =
  | {
      [key: string]: {
        [key: number]: {
          i18nKey: T
          values?: (payload: ApiResponse<T>) => { [key in T]: string }
        }
      }
    }
  | {
      [key: string]: string
    }

const someFun2 = <T extends string>(path: string) => {
  let _payload: ApiResponse<T> | undefined
  const codes2: APIERRORCODES3<T> = {}

  const codesKey = Object.keys(codes2).find((k) => RegExp(k).test(path)) as keyof APIERRORCODES3<T> | undefined // unsure why it cant infer this

  const _code = codesKey && codes2[codesKey]

  if (_payload && _code && typeof _code === 'object') {
    const _value = _code[100].values && _code[100].values(_payload)
    return _value
  } else {
    return undefined
  }
}

const test = someFun2<'A'>('/A')

Since yours payloads appears to always be an object with different keys, I've made an generic ApiResponse<T> that pass T as an obligatory key. Since i also imagine that your api errors will have a default format, I've created APIERRORCODES3<T extends string> that receives it's format but needs a check to be sure that it's correct(i'm guessing it will be received externally). Also, you change it to be the preferred object or undefined instead of what i did. I just did it this way so i can declare it as a variable {} to test the function typing. When getting it from a request, you can change for what bests suits you. Make some runtime type checking, and it returns the payload with the key passed as a generic. If i'm missing something or you need more help, just let me know.

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Type A is not assignable to type A & B & C. Not sure why ts infers with an `&` and not `|`