I just started playing with Flutter, and the most obvious stuff is setState. Honestly, it does not look good. Why would you want to put all your mutations into a lambda, especially if they are all side-effecting? Wouldn't it be better just to call update() directly after you do all the state mutations?

The pattern looks like it came from a functional architecture, but the main point is missing - state mutation should have been encapsulated inside setState function, but this is not the case for Flutter. Without immutability, pure lambda and state change encapsulation all of this doesn't seems have any meaning.