Nuxt•9mo ago

Typescript nested generic resolves to unknown

Am I missing something? In the following example, shouldn't the type of result resolve to { test: { title: 'test' } }? Instead it says it's of type Record<string, unknown>

function test<T, K extends { nested: Record<string, T> }>(data: K) {
  return data.nested;
}

const testdata = {
  nested: {
    test: {
      title: 'Test',
    }
  }
}

const result = test(testdata);

function test<T, K extends { nested: Record<string, T> }>(data: K) {
  return data.nested;
}

const testdata = {
  nested: {
    test: {
      title: 'Test',
    }
  }
}

const result = test(testdata);

Did I reach the limits of Typescript?

Solution:

In the end I actually went with this: ```ts export default function useTranslation() { const { locale } = useI18n(); ...

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5 Replies

GerbuuunOP•9mo ago

Here is a reproduction with more context. I have created three solutions but only one does what I want: https://stackblitz.com/edit/vitejs-vite-xkeyve?file=src%2Fmain.ts

Gerben Mulder

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JuanP Barba•9mo ago

The problem at this example is with K definition. Typescript is not able to infer value of T from generic K definition. You should pass this directly to the argument: https://www.typescriptlang.org/play?#code/GYVwdgxgLglg9mABFApgZygHgCoD4AUAJgIZTEBciA3omOqoZQEooRwBOhmG7MYA5gBpEeRAF8AlNQBQiROxRQQ7JCTIA6OhhSEA3NLHTpbMBmT01xRAF4ZcrQ0pVZc8xicvXyGFAA2KSgBybHpAwU9xF0NDYwQzBTQQXygbNyh8VAxLCV0gA

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JuanP Barba•9mo ago

As you are passing the infer to the method argument, you can see how the infer is ok. I would go with solution one.

GerbuuunOP•9mo ago

Somehow missed that option. Thanks!

Solution

Gerbuuun•8mo ago

In the end I actually went with this:

export default function useTranslation() {
  const { locale } = useI18n();

  type Translatable<K, T> = K & { translations: Record<string, T> };
  function translate<T, K>(data: Translatable<T, K>) {
    const { translations, ...rest } = data;
    const definedLocales = computed(() => Object.keys(translations));
    const translation = computed(() => definedLocales.value.includes(locale.value) ? translations[locale.value] : translations[definedLocales.value[0]]);
    const result = computed(() => ({ ...rest, ...translation.value }));

    return toReactive(result);
  }

  return {
    translate,
  };
}

export default function useTranslation() {
  const { locale } = useI18n();

  type Translatable<K, T> = K & { translations: Record<string, T> };
  function translate<T, K>(data: Translatable<T, K>) {
    const { translations, ...rest } = data;
    const definedLocales = computed(() => Object.keys(translations));
    const translation = computed(() => definedLocales.value.includes(locale.value) ? translations[locale.value] : translations[definedLocales.value[0]]);
    const result = computed(() => ({ ...rest, ...translation.value }));

    return toReactive(result);
  }

  return {
    translate,
  };
}

It is a translate composable which uses the current locale given by Nuxt i18n. I tried function translate<T>(data: { translations: Record<string, T> }) but that resolved to object instead. See final options on typescript play

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Typescript nested generic resolves to unknown