Can you create types with dynamic literals?

SynthLuvr · 2024-06-12T14:25:32.359Z

Say I have this function: ```ts const createType = <T extends string>(code: T) => { const literal: string = code; return type({ code: `'${literal}'` }); }; ``` With this I'm trying to create types with literals but I don't know those literals until runtime. If I run: ```ts const TypeONE = createType("ONE"); ``` It creates type: ```ts const TypeONE: Type<{ code: string; }, {}> ``` But instead what I'm actually wanting is: ```ts const TypeONE = type({ code: "'ONE'" }); ``` Which produces the correct type: ```ts const TypeONE: Type<{ code: "ONE"; }, {}> ```

Say I have this function:

const createType = <T extends string>(code: T) => {
  const literal: string = code;
  return type({
    code: `'${literal}'`
  });
};

const createType = <T extends string>(code: T) => {
  const literal: string = code;
  return type({
    code: `'${literal}'`
  });
};

With this I'm trying to create types with literals but I don't know those literals until runtime. If I run:

const TypeONE = createType("ONE");

const TypeONE = createType("ONE");

It creates type:

const TypeONE: Type<{
    code: string;
}, {}>

const TypeONE: Type<{
    code: string;
}, {}>

But instead what I'm actually wanting is:

const TypeONE = type({
  code: "'ONE'"
});

const TypeONE = type({
  code: "'ONE'"
});

Which produces the correct type:

const TypeONE: Type<{
    code: "ONE";
}, {}>

const TypeONE: Type<{
    code: "ONE";
}, {}>

23 Replies

ssalbdivad•7mo ago

Try:

code: `'${literal}'` as const

code: `'${literal}'` as const

This is a good approach but also keep in mind I'll be shipping native generics soon to make this more intuitive

SynthLuvrOP•7mo ago

as const still causes it to be string I'll try narrow and pipe

ssalbdivad•7mo ago

Ahh oh well I wasn't sure. Let me take a look I know I did some exploration of which strategies like this TS liked Oh wait You reassigned to string That is why it doesn't work

SynthLuvrOP•7mo ago

const createType = <T extends string>(code: T) =>
  type({
    code: type("string")
      .narrow((s) => s == code)
      .pipe((s) => s as T),
  });

const TypeONE = createType("ONE");

const createType = <T extends string>(code: T) =>
  type({
    code: type("string")
      .narrow((s) => s == code)
      .pipe((s) => s as T),
  });

const TypeONE = createType("ONE");

This produces:

const TypeONE: Type<{
    code: (In: string.narrowed) => Out<"ONE">;
}, {}>

const TypeONE: Type<{
    code: (In: string.narrowed) => Out<"ONE">;
}, {}>

ssalbdivad•7mo ago

Realistically '${string}' could validate but doesn't currently That would be the easiest thing For now you can just do this to work around it:

const createType = <T extends string>(literal: T) =>
    type({
        code: `'${literal}'` as type.cast<T>
    })

const createType = <T extends string>(literal: T) =>
    type({
        code: `'${literal}'` as type.cast<T>
    })

Even without the cast it actually is inferred correctly it just doesn't like the validation so you could also ignore the error or something if you wanted When you reassign a variable with an explicit type like this:

 const literal: string = code;

 const literal: string = code;

Whatever previous narrowed type it had is erased, in this case the association with the generic parameter

SynthLuvrOP•7mo ago

Ok yes that works

ssalbdivad•7mo ago

I guess I can't guarantee '${string}' is valid because it could have single quotes Meh

SynthLuvrOP•7mo ago

Seems to behave differently within scope:

const createType = <T extends string>(code: T) => {
  const items = scope({
    Item: {
      code: `'${code}'` as type.cast<T>,
    },
    Items: "Item[]>0",
  }).export().Items;
  return items;
}

const TypeONE = createType("ONE");
type TypeONE = typeof TypeONE.infer;

const createType = <T extends string>(code: T) => {
  const items = scope({
    Item: {
      code: `'${code}'` as type.cast<T>,
    },
    Items: "Item[]>0",
  }).export().Items;
  return items;
}

const TypeONE = createType("ONE");
type TypeONE = typeof TypeONE.infer;

This type is valid:

type TypeONE = {
    code: "ONE";
}[]

type TypeONE = {
    code: "ONE";
}[]

However, this doesn't work:

const createType = <T extends string>(code: T) => {
  const items = scope({
    Item: {
      code: `'${code}'` as type.cast<T>,
    },
    Items: "Item[]>0",
  }).export().Items;

  type TypeONE = typeof items.infer;
}

const createType = <T extends string>(code: T) => {
  const items = scope({
    Item: {
      code: `'${code}'` as type.cast<T>,
    },
    Items: "Item[]>0",
  }).export().Items;

  type TypeONE = typeof items.infer;
}

It becomes:

type TypeONE = {
    code: _distill<T, "out", "base">;
}[]

type TypeONE = {
    code: _distill<T, "out", "base">;
}[]

ssalbdivad•7mo ago

It still looks right to me, it doesn't make sense to have the type be something specific inside the function

const createType = <T extends string>(code: T) => {
    const items = scope({
        Item: {
            code: `'${code}'` as type.cast<T>
        },
        Items: "Item[]>0"
    }).export().Items

    type TypeONE = typeof items.infer
    return items({})
}

const r = createType("foo")

// R is typed as 

type R = ArkErrors | {
    code: "foo";
}[]

const createType = <T extends string>(code: T) => {
    const items = scope({
        Item: {
            code: `'${code}'` as type.cast<T>
        },
        Items: "Item[]>0"
    }).export().Items

    type TypeONE = typeof items.infer
    return items({})
}

const r = createType("foo")

// R is typed as 

type R = ArkErrors | {
    code: "foo";
}[]

SynthLuvrOP•7mo ago

hmm. It's working for me without the scope, but I'm getting type error when using scope:

Type '{ message: string; code: T; }[]' is not assignable to type '{ message: string; code: _distill<T, "out", "base">; }[]'.

Type '{ message: string; code: T; }[]' is not assignable to type '{ message: string; code: _distill<T, "out", "base">; }[]'.

ssalbdivad•7mo ago

You'll have to send a full repro I don't see a point in creating that intermediate type in the inner function

SynthLuvrOP•7mo ago

const example = <T extends string>(code: T) => {
  const Item = type({
    code: `'${code}'` as type.cast<T>,
  });
  type Item = typeof Item.infer;

  const createItem = (): Item => {
    return { code };
  };

  const Items = scope({
    Item,
    Items: "Item[]>0",
  }).export().Items;
  type Items = typeof Items.infer;

  const createItems = (): Items => {
    return [{ code }];
  };
};

const example = <T extends string>(code: T) => {
  const Item = type({
    code: `'${code}'` as type.cast<T>,
  });
  type Item = typeof Item.infer;

  const createItem = (): Item => {
    return { code };
  };

  const Items = scope({
    Item,
    Items: "Item[]>0",
  }).export().Items;
  type Items = typeof Items.infer;

  const createItems = (): Items => {
    return [{ code }];
  };
};

ssalbdivad•7mo ago

I don't know why TS simplifies it when using Type but not Scope, but it doesn't seem like something that could be changed externally. I'd also say if you're working with generics and nested functions this complex it's probably best to not worry about casting too much as even with no dependencies involved TS has a lot of limitations in that regard Maybe the example is more complex so you need the nested scope in the function, but if not you could also consider just using chaining and composition to build your types E.g. in a case like this you could use:

const Items = Item.array().atLeastLength(1)

const Items = Item.array().atLeastLength(1)

SynthLuvrOP•7mo ago

I don't need the explicit return type there, I was only adding it to make sure my function was returning the correct type. If I infer it after creation then it's as I expect:

type Items = ReturnType<typeof createItems>;

type Items = ReturnType<typeof createItems>;

For some reason it doesn't think the type types match when they do

ssalbdivad•7mo ago

Yeah best not to worry about it haha Like worry the external result is correct But trying to get correct inference in those intermediate steps will not always be possible

SynthLuvrOP•7mo ago

Ok so it's not related to scope, because even Item.array().atLeastLength(1) is throwing the error. It must have something to do with the array

ssalbdivad•7mo ago

I see. This is not a real external issue though right? You can just return your type and it is inferred as expected

SynthLuvrOP•7mo ago

Yes it's not a real problem, I just wanted to do a sanity check on the typing to see if I could get a compile time error if I wrote the return value incorrectly. Run time works as expected

ssalbdivad•7mo ago

I think I know why that's happening based on what you mentioned about the array but it's based on the way inputs/outputs and constraints are extracted from the type representation If you wanted to avoid that error internally you'd have to use type.cast on the array as well, but I wouldn't do that I'd just let the type infer on its own it will be safe that way You can't use the "wrong" return type if you just let it infer itself anyways (or at least if TS is working correctly)

SynthLuvrOP•7mo ago

This is definitely over-engineering haha, but I can get the compile-time checks working with inferences. First create an AssertEqual type:

type IsEqual<T, U> = (<G>() => G extends T ? 1 : 2) extends <G>() => G extends U
  ? 1
  : 2
  ? true
  : false;
type AssertEqual<T, U> = IsEqual<T, U> extends true ? T : never;

type IsEqual<T, U> = (<G>() => G extends T ? 1 : 2) extends <G>() => G extends U
  ? 1
  : 2
  ? true
  : false;
type AssertEqual<T, U> = IsEqual<T, U> extends true ? T : never;

Then compare the type with the inferred type:

type Items = typeof Items.infer;
type createItems = ReturnType<typeof createItems>;
type _ = AssertEqual<Items, createItems>;

type Items = typeof Items.infer;
type createItems = ReturnType<typeof createItems>;
type _ = AssertEqual<Items, createItems>;

If the function differs, then the compiler throws an error Can just add a simple sanity check outside of the function, this works:

const example = <T extends string>(code: T) => {
  const Item = type({
    code: `'${code}'` as type.cast<T>,
  });

  const Items = scope({
    Item,
    Items: "Item[]>0",
  }).export().Items;

  const createItems = () => {
    return [{ code }];
  };

  return {
    createItems,
    Items
  }
};

// Compile-time sanity check
const test = example("test");
(): typeof test.Items.infer => test.createItems();

const example = <T extends string>(code: T) => {
  const Item = type({
    code: `'${code}'` as type.cast<T>,
  });

  const Items = scope({
    Item,
    Items: "Item[]>0",
  }).export().Items;

  const createItems = () => {
    return [{ code }];
  };

  return {
    createItems,
    Items
  }
};

// Compile-time sanity check
const test = example("test");
(): typeof test.Items.infer => test.createItems();

This way it can be assured that the types match. If createItems return type doesn't match the type, then an error will be thrown during compile

ssalbdivad•7mo ago

If you're building stuff complex enough that you need type testing you could also consider attest!

Dimava•7mo ago

Have you considered just using type('===', code)?

aabad_ankit•3mo ago

Thank You. This is what I was looking for.

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Can you create types with dynamic literals?

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