Strange, the IDE inferred unknown when specifying ArrayLength<any>, but tests failed, because there it was inferred as an any type. Updated.

https://github.com/sindresorhus/type-fest/pull/1344/changes#diff-a6653dddc77761046fd084a2c26be9d7c4af1eaf6fc2394dc42d8d7f67281e3cR34 fails.

@jericirenej Updated the implementation of ArrayLength to the following:

export type ArrayLength<T extends readonly unknown[]> = T['length'];

type T = ArrayLength<any>
//=> any

The previous implementation returned unknown when instantiated with any. IMO, returning any is better.

type ArrayLength<T extends readonly unknown[]> = T extends {readonly length: infer L} ? L : never;

type T = ArrayLength<any>
//=> unknown

Also, the updated implementation is much simpler.

@som-sm Looks great, thanks! 👍
I was also curious initially why the original type was inferring the length instead of just accessing length directly. But at that point I did not venture further and just focused on providing some tests and documentation which would satisfy the requirements for the type to be exported.

This possibility of accessing the length directly was also one of the reasons that - when faced with the options to expose the type or remove it - I was leaning more into arguing for its omission in my initial post.

This possibility of accessing the length directly was also one of the reasons that - when faced with the options to expose the type or remove it - I was leaning more into arguing for its omission in my initial post.

I agree, this type isn’t that useful. It’s essentially just syntactic sugar, T["length"] vs ArrayLength<T>. I’m also fine with removing it. @sindresorhus, WDYT?

I think it's useful as documentation. It's easy to say that T["length"] is better, but most don't even know about it. I also find ArrayLength slightly more readable at callsite. So our docs can make it clar that T["length"] is also a good alternative.

Ok, I'll update the base type description and docs later today!

Rebased to current main and updated documentation.

Hopefully the added documentation is clear and concise enough:
Return the length of an array. Equivalent to `T['length']` where `T` extends any array.

Is there anything else that needs to change here or is the current solution good enough for merging @sindresorhus?

Thanks for working on this :)