3. Redux Pilot

Date: 2023-09-07

Status

Approved

Context

Firefox iOS currently relies on MVVM in many areas while a large BrowserViewController (BVC) still coordinates significant logic and state. This leads to:

• Cross-coupled view controllers and ad-hoc delegation chains.
• Race conditions and nondeterministic state transitions.
• State scattered across controllers, view models, and services.
• Navigation and side-effects intertwined with UI logic, making testing hard.

Decision

Adopt a lightweight, in-house Redux-style architecture (inspired by ReSwift’s core types) to be introduced incrementally, starting with a contained feature area.

Main components

• Information flow is structured and always flows in one single direction.
• There is a single global immutable state kept in store.
• New state can be set only by dispatching an action to store and is calculated by reducer which is a pure function.
• Store notifies subscribers by broadcasting new state.

Middlewares

• Middleware is where side effects of actions are managed
• Examples: network requests or reading data from storage
• May send a new action back to the store

Scope (Pilot)

Start with a contained surface (e.g., ThemeSettingsController).

Prove: determinism, testability, and developer ergonomics.

Consequences

Positive

• Deterministic, serial state evolution; fewer races.
• Easier unit/integration testing of state transitions and effects.
• Clear boundaries (reducers vs middleware vs UI).

Negative

• Learning curve and mindset shift for the team and external contributors.
• Boilerplate (actions, reducers, wiring) without helper tooling at first.
• Risk of over-modeling state if guidelines aren’t enforced.
• Migration cost and interim duplication with existing MVVM logic.
• If misused, middleware can accumulate too many responsibilities (must be kept small and focused).
• We need a clear interoperability story with our Coordinator + Router navigation approach.

References

• Redux on iOS
• Investigation
• Implementation Presentation