functions that take in types

type("string[]") // this type is not always the same, can be regex, etc...
    .or("undefined")
    .pipe((v) => v ?? [])
    .narrow(
      (v, ctx) =>
        new Set(v).size === v.length ||
        ctx.mustBe("array with unique elements"),
    )

const uniqueDefaultStringArrayDef = (schema: Type<string[]>) =>
  defaultEmptyStringArrayDef(uniqueStringArrayDef(schema));

const defaultEmptyStringArrayDef = (schema: Type<string[]>) =>
  schema.or("undefined").pipe((v) => v ?? []);

const uniqueStringArrayDef = (schema: Type<string[]>) =>
  schema.narrow(
    (a, ctx) =>
      new Set(a).size === a.length || ctx.mustBe("array with unique elements"),
  );

export const defaultArray = <const def>(input: type.validate<def>) =>
  type(input as type.cast<type.infer<def>>)
    .or("undefined")
    .pipe((v) => v ?? []);