#17910 - Pull Request updated.

type AnyMeasurementUnit<T> = {
  [K in keyof T]:T[K] extends readonly any[]?T[K][number]:never
}[keyof T]

@koodiohto Your description is too specific. It's better to have a broader description

Thank you for your feedback and one possible solution! I'd appreciate if you still have time to point out which part of the description in specific you think should be made broader. Or do you mean that this example shouldn't be coupled to the measurement units, but be more generic? Thanks!

Btw. this is how I ended up solving this (without using generics in the type):

type AnyMeasurementUnit = typeof AllMeasurementUnits[keyof typeof AllMeasurementUnits][number]

@koodiohto

Yesterday I edited your test case from Expect<Equal<AnyMeasurementUnit, 'g' | 'kg' | 'pound' | 'cm' | 'm' | 'inch'>>, to Expect<Equal<AnyMeasurementUnit<typeof AllMeasurementUnits>, 'g' | 'kg' | 'pound' | 'cm' | 'm' | 'inch'>>,. At first I thought it was just a typo. After you replied me , I finally realize that what you want to implement is just a spefic type , and what you described in the Question section is only for this spefic type.

Actually, I hope your type AnyMeasurementUnit to be a generic type , like the built-in Partial<T> type, which accept a type parameter rather than a specific type derived from typeof AllMeasurementUnits . In this way, we can broad the usage of this type.

Then we can use this type like this :

AnyMeasurementUnit<{
   onlyLength: ['m','km']
}>

AnyMeasurementUnit<{
   onlyWeight: ['g','kg']
}>

Okay, thank you for your feedback!

I was just thinking that my original suggestion was based on an actual "business logic need" which was solved by this AnyMeasurementsUnit-type. So I had the case that I needed to categorize the measurements units, but then I also needed a type for checking that the measurement unit is a valid measurement unit, but doesn't matter to which "measurement unit category" it belongs to. So it's more a type that "validated that a type is a value in another object's arrays".

So if I would try to make the question setup in my original idea to be more broader, I would probably propose it to be like this (so it wouldn't be coupled to the measurements units context):

const ObjectWithArrayValues = {
  key1: [1,2,3], // possibly more in the future
  key2: ['one', 'two', 'three']
  //possibly more in the future
} as const

type AnyValueInObjectWithArrayValues= typeof ObjectWithArrayValues[keyof typeof ObjectWithArrayValues][number]

But I definitely agree that I am having hard time of formulating this into an understandable question. And I don't know if this makes for a good general use case with TS that is a good assignment in the first place..?

But yeah, when still thinking of your good proposal, so maybe it is better to change the assignment description and task to utilize this "generic" type that can be used in a similar fashion as the Partial type. I'll try to modify this next week. Thanks!