Can you change the call signature of a function based on whether a generic is undefined?

[daring storm]

This is a simplified version of the scenario I'm contending with written in psuedo code.

function MyHOF<Payload extends object | undefined>(config: {
   payload?: Payload
}) {
    
    // return this if payload isn't configured
    return (config?: {options: any}) => any
    // return this if payload signature is provided
    return (config: {options: any, payload: Payload}) => any
}

I've made several attempts to write this and come up with overly complicated type signatures that don't work. Do I need to do something along the lines of:

type DoAction<Payload> = Payload extends undefined
? { (config?: {options: any}): any }
: { (config: {options: any, payload: Payload}) }

[lone valley]

What about function overload?

[mighty summit]

[Payload] extends [undefined] but yeah

but yeah overloads are a way better idea

[daring storm]

@lone valley Are you saying conditionally create the options and then use overloads to determine the function's signature?

type Config<Payload> = Payload extends undefined
? {options: any}
: {options: any, payload: Payload}

type DoAction = {
  (config?: {options: any}): any
  (config: {options: any, payload: Payload}): any
}

const doAction: DoAction = <Payload>(config?: Config<Payload>) => undefined

[lone valley]

I don't think Config<Payload> is even used anymore then?

You can just do:

type DoAction = {
  (config?: {options: any}): any
  <T>(config: {options: any, payload: T}): any
}

Your doAction arrow function can have whatever type that's convenient for implementation.

[mighty summit]

i think theyre suggesting to use only overloads

[daring storm]

I think that my contrived example didn't fully illustrate the issue. What I ended up with was this:

type WithParams<TParams> = TParams extends undefined ? {}
    : { params: TParams };

type WithPayload<TPayload> = TPayload extends undefined ? {}
    : { payload: TPayload };

type Config<TParams, TPayload> = {
    axios?: AxiosRequestConfig;
} & WithParams<TParams> &
    WithPayload<TPayload>;

type DoFetch<TParams, TPayload, TResponse> = TParams extends undefined
    ? TPayload extends undefined
        ? { (config?: Config<undefined, undefined>): TResponse }
        : { (config: Config<undefined, TPayload>): TResponse }
    : TPayload extends undefined
    ? { (config: Config<TParams, undefined>): TResponse }
    : { (config: Config<TParams, TPayload>): TResponse };

I feel like there's a better way, but this works the way I wanted it to. doFetch is nested inside a HOF that receives a default configuration object where all of these types are inferred. The doFetch config and call signature shapes are tightly coupled to the shape of the default configuration.

If TParams or TPayload are defined, then you HAVE to provide a config to doFetch that includes those, otherwise it's optional (as a passthrough for the axios config).

[lone valley]

You should make a TS playground that includes all the relevant types and how you expect the consumer to use your API.

You are only giving bits and pieces each time and the conversation has to keep going back and forth to fish out more information.

[daring storm]

@lone valley Here's the current iteration of the code.
https://www.typescriptlang.org/play?#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-82LHkwkctsAG4UKBhhwW2owrixt5YPJN53YPaadAGsESSEMZjsLimuA4yO210DzLYvar6P9RtF0XdxYAEQg3n4co3sSHu9EhsO2ooieFbtO9PT32EezZw6LZffjKft+xgpH4facAa86wsEgE+lgsHMnEBRUgcRyyLmnT5qB4E5FB-YIU8SYHsh95ofIeZEVK-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-QI0q0xBjIDt5S7wgNQ4+2jdq8Cw2RyQIEVCDAktAgrQN0zq3QDB7YHp2vcaF2TFdX2uJbi01jMdYNhTcMyJLqeYT9AP7UDcv7ej0y5RBq3iKj9cY5sWM48JbeLRSWR5-tPYQDbFJJIkyRqJ5nOiywaiD4HiuxdlgiyH4-kG-Kmox7IY-Tzt2VxXALAQPAZveRUC-7UvWvXjHR-rzQMjjCfsVoGgSdX-nqxeCk3tcv5RAEUCgsg9q6AoX9K4UjznIf2ecl7W0QHAUOj43ZwEjuMMAyhWzAA2LsVOS9Ggf23qvZBlM4DCFUggOAioYBynoLFGAedEEpBQfDehip5oLyXpqDqXBsoQGUmAZScAR4FigDITs5QcobzRjAaI0g2DQFUBg1YMg6IVzYTIaYlCVLOi0RQN2YCJEUFYZTHRVD-apy2qnDKWUyGlxNDzM0AcFZK16kzFgVh4D1AANayGWuMAARiI7qVhVAn3gMQ2QQgipLQgHATg-AeZL1IWgfhqlVbjECDQ1ScoeZ2KgNlJm546Gs0AaeUpl486WRqbeXuZUVBxQoCnVO0504yFaRXEuZF3qek+vMGoX8C7CGmEXMIHSnxfxyMdCui1wpOAXuXQOyzOiHk6LmLaS8ADEuztlwAAKIAA08A8HCAAGQOboBmiAwDAGdNsOJXVurTXEBA65wc4A8CcGg5IJhpgQCCQAK3NjAYGPMWDaxyP8jkFQUgFFRlg1AZRnDQumCwGgIAgkdnhfjd5Nz6gMHWnc1aB9wXI0pHAAABqMSA5QYBUuhvidEOQrAAHEDmhCsNDAxbsiQ-I4QgVaUBohVQgbAhwNyaBgF0bIcOJL+TqXJT-SlwNYoDAJsYXBORYVclgcUaltKID0vlgAEmwLguQjK8RokJHAKw4R-jSi5dDX2fKvkCr1AgXQErdDStlWq2+g1cDavtQARgjWGqw8gsC+3zJC1ErKRgMG5eKMo0BgROByGG8wEql7+tUqYooABaYty9WwIHqHeROwBYZwCCafVmQagEDGob7XQhKwXYBmjgIqNpGCag2E0YAlbBryLoHICVnb4VwCXhWqtWB0mcwCfKRA4gcrgTfqIsAs9K0tuPgkxtHZxE0n1mQ2gtadhAA

Ooof, is there a better way to format that link?

The consumer side of things seems to be correct at this point, but the Typescript is hideous and clunky.

[lone valley]

If you post the link as a separate message then TS bot will shorten it for you.

[mighty summit]

😔 nitro problems

[daring storm]

https://tenor.com/view/sad-walk-gif-24718162

I only got nitro so I could post that link....

[mighty summit]

moment

it actually works better

(or at all)

without nitro

the bot doesn't work with >2000 char (aka nitro) messages, but it does work with messages sent as text files

[daring storm]

https://tenor.com/view/computer-stick-man-table-flip-look-at-you-9gag-gif-26257332

[mighty summit]

has to be named message.txt

[daring storm]

A file, named message.txt, with the link as the contents?

[mighty summit]

yeah

without a trailing space and without a trailing newline

[mighty summit]

😔