Feature Discussion: Slice selector behavior with combineReducers

[nmastereal]

Slices have been a great improvement in our code base for isolating all the previous patterns (actions / action creators, reducers, selectors) to slices. The last piece we are looking to isolate is selecting sub-state in a slice when using combineReducers in a tree structure. It seems that the slice's exposed selector expects the state to be the parent relative to that slice but in the connect function from react-redux we are given the rootState. With the rootState we have to know how to get to the sub-state where the slice lives.

I've read several thoughts on here about combineSlices which could be a good approach to solving this. The slice could then expose a function which given a rootState knows how to return the slice.

Our example state tree:

- rootState
   - screens
      - screen1
      - screen2
           - userName
           - userEmail

so if we had a slice for screen2, the connect function on screen2 looks something like:

connect(
     (rootState) => ({
             userName: rootState.screens.screen2.userName
     },
     {
             setUserName: slice.actions.setUsername,
     },
)(screen2Component);

This means the component needs to know the structure of the state. Instead you could imagine something like:

connect(
     slice.selector,
     slice.reducers,
)(screen2Component);

or

connect(
     (rootState) => ({
             userName: slice.selector(rootState).userName
     },
     {
             setUserName: slice.actions.setUsername,
     },
)(screen2Component);

Any thoughts or ideas? I am definitely willing to help work on solving this. I want to minimize the amount of places that know the structure of the actual state. Leaving structure to combineSlices
alone seems to be the best bet.

[markerikson]

I really don't have any good answers on this. This is basically the "encapsulated selectors" question, which Randy Coulman wrote about here and the other linked posts:

Solving Circular Dependencies in Modular Redux.

[markerikson]

Coming back around to this. I think the conclusion is that we're going to remove any slice-specific selector functionality, and leave it up to you to define whatever selectors you feel are appropriate, same as with any other Redux app. (See #91 for some related thoughts.)