Can we change Reducer from protocol into function type? about reswift HOT 10 CLOSED

I believe @agentk was in favor of this as well. If that's the case I'd be happy to deprecate the Reducer protocol with the next release and add support for free functions.

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Yes, we could potentially do this! The reducer protocol is an artifact from an older ReSwift version. One of the advantages of using a type instead of a free function is that the error message around type mismatches in the store and the root-reducer is slightly better.

However, our docs have been suggesting using free functions for any but the root reducer function; so it might be more consistent to change this.

I don't have a strong opinion either way. I would love to see the change on a branch to see the impact it would have.

@ReSwift/reswift any opinions on this?

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A reducer type doesn't have much value in my app TableFlip so far compared to a free function. So I think this is okay. Where the function lives is up to the team anyway -- they could create a Reducers struct with static functions and reference these, for example.

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I also agree that they should be free functions 👍

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I like the idea of deprecating Reducer, but what I like even more is turning Reducer into a concrete struct that allows mapping and concatenating Reducers with ease. I've implemented this in ReactiveReSwift and I'm very happy with the results. Here's a reimplementation of the GitHub Example code using this new structure.

let appReducer = Reducer(authenticationReducer, bookmarksReducer, repositoriesReducer)

let authenticationReducer = Reducer<State> { action, state in
    var state = state

    switch action {
    case let action as SetOAuthURL:
        state.authenticationState.oAuthURL = action.oAuthUrl
    case let action as UpdateLoggedInState:
        state.authenticationState.loggedInState = action.loggedInState
    default:
        break
    }

    return state
}

let bookmarksReducer = Reducer<State> { action, state in
    var state = state

    if let action = action as? CreateBookmark {
        let bookmark = (route: action.route, routeSpecificData: action.routeSpecificData)
        state.bookmarks.append(bookmark)
    }

    return state
}

let repositoriesReducer = Reducer<State> { action, state in
    var state = state

    if let action = action as? SetRepostories {
        state.repositories = action.repositories
    }

    return state
}

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@Qata agree that this looks nice! One thought: using only functions it's easy to compose reducers that operate on a substate of the overall state. E.g. in the GitHub example we only pass the bookmark state to the bookmark reducer. This enforces separation of concerns within reducers. Do you have an idea if/how this would be possible with your approach?

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Finally opened #177, that serves the original request of making Reducer a function type. While I'm a big fan of @Qata suggestion of revamping the middleware API (#175). I think that having the reducer being a function type has advantages for composition that I mentioned above.

You can see an example here: https://github.com/ReSwift/GitHubBrowserExample/blob/master/SwiftFlowGitHubBrowser/Reducers/AppReducer.swift#L16-L19

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Shipped with #177.

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