Ergonomic State Management: Part 1

Exercises

1. Now that the Reducer type is a proper struct we can provide specialized initializes for common use cases. For example, it often happens that a reducer doesn’t need to do any side effects, and therefore it doesn’t need to return anything and its environment could be Void. Create an initializer on Reducer for when Environment == Void that allows us to create a reducer without having to worry about side effects.

   Solution

   extension Reducer where Environment == Void {
     init(_ reducer: @escaping (inout Value, Action) -> Void) {
       self.reducer = { state, action, _ in
         reducer(&state, action)
         return []
       }
     }
   }
   

2. Continuing the previous exercise, there is another form of reducer that some may like more than our current shape. Right now we have immediate access to the environment in the reducer, which means we technically could invoke the effects right there in the reducer. We should never do that, but it’s technically possible.

   There is a slight alteration we can make to the reducer so that it is not handed an environment, but instead it will return a function that takes an environment and then returns effects. Create a static function on Reducer called strict that allows one to create reducers from that shape.

   Solution

   extension Reducer {
     static func strict(
       _ reducer: @escaping (inout Value, Action) -> (Environment) -> [Effect<Action>]
     ) -> Reducer {
       .init { value, action, environment in
         reducer(&value, action)(environment)
       }
     }
   }