FeatureModulesExampleApp

Sample app for the article "Assembling little building blocks into a functioning banking app". It shows how features are split into Swift packages and how they talk to each other, without ever compiling each other's implementation.

It reuses the domain of UnownedCoordinatorExampleApp: Swiss cities, their events, and a modal to add one. Coordinators follow the same UnownedCoordinator model: views own their coordinators.

Run it

Open FeatureModulesExampleApp.xcodeproj (Xcode 26+), select the ExampleApp scheme and run. ⌘U runs the FeatureModulesExampleApp test plan, with every layer's test target.

How the features use each other

flowchart LR
    App["App target<br/>(the monolith)"] -->|registers| Home & Details & AddEvent
    App -->|implements| AppAPI["AppEventDetailsFeatureAPI<br/>(App package)"]

    Home["HomeFeature"] -->|uses| DetailsAPI["DetailsFeatureAPI"]
    Details["DetailsFeature"] -->|uses| AddEventAPI["AddEventFeatureAPI"]
    Details -->|uses| AppAPI
    AddEvent["AddEventFeature"]

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Feature	Kind	Uses
AddEvent	Standalone	nothing
Details	Consumer	AddEvent, EventDetails (through the App package)
Home	Consumer	Details
EventDetails	Not modularised yet	lives in the app target

Where to look

Article section	In this repo
Internal anatomy of a feature	Features/Details/Package.swift: one target per layer (Requests, Domain, Data, Presentation) and one test target per layer
Common packages	Common/Domain (shared City and Event), Common/Navigation, Common/ModuleLoader
How features talk to each other	Features/*/Sources/API (protocols only) and Features/*/Sources/<Name>/<Name>FeatureModule.swift (hidden implementation)
Dependency injection	Common/ModuleLoader (CommonModuleLoader, @YuhFeature), registrations in App/AppDelegate.swift, usage in HomeCoordinator and DetailsCoordinator
What if the App itself was a temporary feature?	Features/App (API-only package) and App/AppDelegate+AppEventDetailsFeatureAPI.swift
Testing each block	FeatureModulesExampleApp.xctestplan

Layers inside a feature

flowchart TD
    subgraph Details["DetailsFeature"]
        Presentation["DetailsFeaturePresentation"]
        Data["DetailsFeatureData"]
        Domain["DetailsFeatureDomain"]
        Requests["DetailsFeatureRequests"]

        Presentation --> Data
        Presentation --> Domain
        Data --> Domain
        Data --> Requests
    end

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A layer only exists when a feature needs it. AddEvent doesn't fetch or store anything, so it has no Requests or Data layer.

Building a feature on its own

Each feature package builds without the other features' implementations:

cd Features/Details
xcodebuild -scheme DetailsFeature -destination 'generic/platform=iOS Simulator' build

The build output only contains AddEventFeatureAPI and AppFeatureAPI from the other features, never AddEventFeature itself.

Moving EventDetails out of the monolith

1. Create Features/EventDetails with the same layers.
2. Move AppEventDetailsFeatureAPI there and rename it to EventDetailsFeatureAPI.
3. Register EventDetailsFeatureModule() in AppDelegate, instead of self.
4. In DetailsCoordinator, only the protocol name changes.