[valenterry]

> This makes union types unsound in the presence of type parameters/generics.

I'm not sure if "unsound" is a good adjective here. There are cases where this is actually desired behaviour and the rules can definitely be "sound".

For example, I might want to know what errors can appear, but not care where they come from. So `ErrorA | ErrorB` is what I want to see, not some nested structured that allows me to differentiate where ErrorA came from in case that there are multiple possible options.

[ObscureScience]

I did not catch from you comment if you knew, but "sound" and "unsound" are specific concepts in type theory, and they are binary properties. A system either is or is not sound.

[valenterry]

Yeah I know that.

So: > This makes union types unsound in the presence of type parameters/generics.

Sounds a bit strange to me. Why would union types + type parameters be generally unsafe? I doubt that that's true.

[trenchgun]

Sound type system is not one of the design goals of TypeScript

https://effectivetypescript.com/2021/05/06/unsoundness/