A
arktype•2mo ago
Robb

About using a generic pipe

Hello everyone, I am writing a schema in which one of the fields requiredness can be played with. I've come up with this type 
const StringWithOptionalModification = type({
  value: "string",
  mode: "'required' | 'on' | 'off'",
}).pipe((obj) => {
  return obj.mode === "off" ? null : obj.value;
});
const StringWithOptionalModification = type({
  value: "string",
  mode: "'required' | 'on' | 'off'",
}).pipe((obj) => {
  return obj.mode === "off" ? null : obj.value;
});
It does the job perfectly well. Now, if I want to use it for a schema, where the value should be sent if the value is null, I can use something like this: 
const Profile = type({
  username: "string",
  password: StringWithOptionalModification,
  firstName: "string",
  lastName: "string",
}).pipe((s) => {
  const { password, ...rest } = s;
  const passwordObj = password !== null ? { password } : {};
  return {
    ...rest,
    ...passwordObj,
  };
});
const Profile = type({
  username: "string",
  password: StringWithOptionalModification,
  firstName: "string",
  lastName: "string",
}).pipe((s) => {
  const { password, ...rest } = s;
  const passwordObj = password !== null ? { password } : {};
  return {
    ...rest,
    ...passwordObj,
  };
});
But now, let's say I want to reuse this kind of logic in multiple other schemas. I thought about creating a pipe generator so that only the key needs to be set. Something like this: 
const generateEmptyPasswordRemovalPipe = (key: string = "password") => {
  return (s: { [key: string]: string | null }) => {
    const { [key]: password, ...rest } = s;
    const passwordObj = password !== null ? { [key]: password } : {};
    return {
      ...rest,
      ...passwordObj,
    };
  };
};
const generateEmptyPasswordRemovalPipe = (key: string = "password") => {
  return (s: { [key: string]: string | null }) => {
    const { [key]: password, ...rest } = s;
    const passwordObj = password !== null ? { [key]: password } : {};
    return {
      ...rest,
      ...passwordObj,
    };
  };
};
that would help by rewriting Profile as 
const Profile = type({
  username: "string",
  password: StringWithOptionalModification,
  firstName: "string",
  lastName: "string",
}).pipe(generateEmptyPasswordRemovalPipe("password"));
const Profile = type({
  username: "string",
  password: StringWithOptionalModification,
  firstName: "string",
  lastName: "string",
}).pipe(generateEmptyPasswordRemovalPipe("password"));
But then, the types resulting from the schema seem off. I guess this is more a TypeScript-related question than a Arktype one
1 Reply
ssalbdivad
ssalbdivad•2mo ago
Yeah this kind of stuff can definitely be tricky. Especially as your generic logic gets more complex, you will likely have to write the type-level logic manually using conditionals + mapped types to achieve what you want, then cast your implementation to that specified return type. I wrote a bit about this in the docs here: https://arktype.io/docs/faq#why-isnt-my-wrapper-generic-working
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