AppState's Just‐In‐Time Creation of Values

AppState, a Swift Package for managing application state, introduces "Just-In-Time" creation. This method optimizes resource usage and enhances application performance. This article provides a detailed overview of just-in-time creation in AppState, explaining its workings, benefits, implementation, and potential use cases.

Understanding Just-In-Time Creation

Just-in-time creation in AppState is a process where values, including State, Dependency, StoredState, and SyncState, are instantiated only when first accessed. This method prevents AppState from consuming unnecessary resources, improving efficiency and performance.

Benefits of Just-In-Time Creation

The key benefit of just-in-time creation is efficient resource usage. AppState uses resources only when needed, improving performance, especially in applications where numerous states and dependencies are defined, but only a subset are used during a particular session. It can also improve startup performance by reducing the initial load time of the app.

Implementing Just-In-Time Creation in AppState

AppState implements just-in-time creation using Swift's property wrappers. When State, Dependency, StoredState, or SyncState are defined in your AppState, these values are not instantiated until first accessed.

For instance, consider a State defined in AppState:

extension Application {
    var defaultState: State<Int> {
        state(initial: 0) // The value is not created until it's accessed
    }
}

In this example, defaultState is not created until it's accessed for the first time. This illustrates just-in-time creation in AppState.

Just-in-time creation is useful in applications with large AppState or a significant number of dependencies. By creating values only when needed, it helps manage resource usage and improve application performance. It also ensures values used under specific conditions are not instantiated unnecessarily.

Preloading Dependencies with AppState's Load Function

AppState provides a method to preload dependencies using its load function. This function initializes certain dependencies before they are used in your view code, beneficial for dependencies requiring time to initialize or needing to be available when your application starts.

For instance, you might have a database client dependency that takes time to establish a connection. With AppState, you can use the load function to preload this dependency when your application starts.

Here's an example:

extension Application {
    var databaseClient: Dependency<DatabaseClient> {
        dependency(DatabaseClient())
    }
}

// Then somewhere in your app initialization code, you can load the dependency:
Application.load(dependency: \.databaseClient)

In the above example, databaseClient is preloaded when the application starts by calling load(dependency: \.databaseClient). AppState ensures that it retrieves the already initialized DatabaseClient when you later access databaseClient in your view code.

By using the load function to preload dependencies, AppState helps manage the initialization of your dependencies and the resources they use. This ensures that your views have immediate access to fully initialized dependencies when needed.

Conclusion

AppState's just-in-time creation of values offers a unique way to manage application state and dependencies. By creating values only when needed, it optimizes resource usage and enhances application performance. Understanding just-in-time creation in AppState can help you effectively use this feature in your apps.