I suppose. In practice, I haven't experienced this to be a problem. Since you already check which implementation you are dealing with, any code that relied on a

I suppose. In practice, I haven't experienced this to be a problem. Since you already check which implementation you are dealing with, any code that relied on any state, should still work without any issue. This is the same as with typescript unions. Any code that somehow needs to handle a new state hm... I suppose getting a compile time error is nice to immediately see all places where it is used... but, I mean, so would a "find all uses" search. It's also not all that different from the linting warning error you'd get from iterating over runtime types without handling all cases. All in all, sufficiently analogous to not consider unions a missing feature of the dart language? Seems nice to have, but, maybe not very necessary. Especially if the only difference is whether it is considered an error by the syntax, or a warning by the linter.