Question about useReducerAtom and derived atoms

[mo-lon]

Hi All - i'm starting out with Jotai and had a question around re-renders and usage of useReducerAtom in this contrived example

https://codesandbox.io/p/sandbox/inspiring-haze-37n98f

I would have expected the components to only re-render when their state changed but doesnt look like thats the case. The atoms are derived from state slices and the overall state is updated by the dispatcher

[rothsandro]

Your useReducerAtom hook reads the whole atom state, that's why the component re-render. Replace it with useSetAtom which doesn't return the atom value:

- const [, setState] = useAtom(anAtom);
+ const setState = useSetAtom(anAtom);

[mo-lon]

Thanks, that did the trick