API: Reducer Composition Helpers

Combines multiple reducer functions into a single reducer function. Each reducer function must reduce the same type.

Usually, you will want to to convert multiple key-specific reducers into a single reducer to represent an entire type using forKey(_:use:).

struct Scoreboard {
    var home = 0
    var away = 0
}

let scoreboardReducer: ReducerFn<Scoreboard> = combineReducers(
   forKey(\.home, use: homeScoreReducer),
   forKey(\.away, use: awayScoreReducer)
)

Convert a reducer function for a specific instance property into a reducer function for the entire instance.

Usually paired with combineReducers(_:).

The following example converts a reducer that only reduces the home score into a reducer that reduces the entire Scoreboard:

struct Scoreboard {
    var home = 0
    var away = 0
}

let homeScoreReducer: ReducerFn<Int> = { (state: Int, action) in
    var state = state
    switch action {
        case let action as HomeScore:
            state += 1
            return state
        default:
            return state
    }
}

let homeKeyReducer: ReducerFn<Scoreboard> = forKey(\.home, use: homeScoreReducer)