The Best API Change Is the One Nobody Notices

Scene-aware custom containers in Factory, and the design that let the existing API stay put…

Michael Long

6 min read

·

Oct 22, 2026

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Every library author eventually learns that new capability costs new API.

A new feature means a new parameter, a new generic, a new protocol requirement, and a migration guide for everyone who already depends on you. It’s practically a law of nature.

Sometimes.

In my last article I introduced scene-based injection for Factory’s default container. It left a gap, and closing that gap looked like it was going to break things. It didn’t, and the reason why is worth a look.

The Gap

Here’s what scenes gave us. Install a Container at the root of each window, publish it in the environment, and @InjectedObject and @InjectedObservable resolve from it instead of Container.shared.

@main
struct DemoApp: App {
    var body: some Scene {
        WindowGroup {
            SceneRoot()
        }
    }
}

struct SceneRoot: View {
    @State private var sceneContainer = Container()
    var body: some View {
        ContentView()
            .withContainer(sceneContainer)
    }
}

struct ContentView: View {
    @InjectedObservable(\.contentViewModel) var model
    var body: some…