support literal type in eb.case

[pyb0987]

Hi, thank you for making and developing this amazing library!
I think this might enhance type guard of kysely.

      eb
        .case()
        .when('user.height', '>=', '170')
        .then('tall')
        .else('short')
        .end()
        .as('desc') // this returns type desc: string

I hope this return 'tall' | 'short'.

[koskimas]

Does it work if you use 'tall' as const and 'short' as const?

[igalklebanov]

Hey 👋

For now, what @koskimas suggested works.

In the future, we could use const type parameters in then and else, to provide a tighter experience. These modifiers were introduced in TypeScript 5.0, released on March 16th, 2023.

The case builder was built around a time when that TypeScript version was less than a month old (too new).

According to some processing I did, moving from 4.7 as the minimum TypeScript version to 5.0 is a move from ~85% of the weekly TypeScript downloads to ~64% of the weekly TypeScript downloads.