Unidirectional Data Flow test project

This is a sandbox project to come up with an entry level unidirectional data flow app, without using any frameworks. The end goal is to come up with a very simple architecture that both communicates the core principles behind unidirectional data flow, and is safe to publish as a tutorial (ie in case developers drop it into their own projects as is).

The app uses Realm for state storage, and only attempts to show a unidirectional flow relating to a single view. Navigation/Routing is a whole other bag of hurt.

Core Components

1. Store: This is a wrapper around the realm instance, manages state updates & change notifications. A global instance is declared with the name store.
2. StoreSubscriber: A protocol enabling subscription to state changes.
3. Action: An enum with a case for each state change action that can be performed on the store
4. TodoItem: The model, a Realm Object subclass.
5. ListItemViewController: A UITableViewController that handles displaying and editing the todo items.

Smells/alternatives/stuff not done that maybe should be

• Todo app - sorry, the tutorial definitely won’t be one of these.
• Global store variable - most Cocoa devs would maybe be more comfortable with a singleton?
• The weak hashset subscriber implementation - this was the simplest implementation I could think of, but it doesn’t necessarily mean it’s the simplest to understand. Maybe an NSNotification or a single delegate would be sufficient to illustrate the concepts.
• The reducer functions are defined as private functions in the Store class. This isn’t how it’s normally done, but it seems to make more sense to me to do it this way given its a DB update rather than a transform over a value type.
• Materialising the Realm allObjects as an array. Again, this seems to make the most sense in the context of this app, but most apps won’t have a single array as their app state and maybe the tutorial demo should include more data types. This may end up impacting the reducer design?
• No thread-handling, although under this design it’s relatively straightforward to confine the realm updates to a specific queue and it might be good to add this at the end of the tutorial.
• There’s some local state sprayed across the view controller; I’m currently just wiping this on update, but it might be worth explicitly modelling the local state in the VC React-style.

I’ll obviously want to point people to the frameworks at the end (esp reactive frameworks rather than writing your own multicast events). This is still a work in progress so I’m open to suggestions & improvements.