Zod 2 beta 5: applying transform() to arrays

Hi,

I’m trying to use .transform() on a string array to remove possible duplicates. This is my schema:

DummyInput = z.object({
  pokemonTypes:
    z.array(string())
    .nonempty()
    .transform(cleanDuplicateStringsFromArray)
})

The function signature is (array: string[]) => string[]. Seems right - take an array of strings and transform it to itself… although I get an error:

TS2345: Argument of type '(array: string[]) => string[]' is not assignable to parameter of type '(arg: [string, ...string[]]) => string | Promise<string>'.   Type 'string[]' is not assignable to type 'string | Promise<string>'.     Type 'string[]' is not assignable to type 'string'.

Am I missing something here?

[tmtron]

Sice you call .nonempty(), your input type is not just a string[], but the tuple [string, ...string[]].

Per default, the transformer function must also return the same type (but you could override it), so your transformer function could be like this:

function cleanDuplicateStringsFromNonemptyArray(arg: [string, ...string[]]) {
  // get an array of distinct items
  const distinctItems = [...new Set(arg)];
  // destructure array to match output type
  const [first, ...rest] = distinctItems;
  return [first, ...rest];
}

[colinhacks]

Thanks @tmtron!

@grreeenn there probably shouldn’t be a difference but I guess it worked out in your case. If anyone else is unhappy with the typing of .nonempty feel free to implement your own validation logic with .refine (which never changes the inferred type).