How to improve SwiftUI’s AppStorage property wrapper

AppStorage is the easiest way to access UserDefaults in SwiftUI. It works like State and automatically retrieves and updates the underlying UserDefaults data. It is used as such:

struct ContentView: View {
    @AppStorage("SHOW_SPLASH_SCREEN") var showSplashScreen = true

    var body: some View {
        // content
        .sheet(isPresented: $showSplashScreen) {
            // splash screen
        }
    }
}

Here, the "SHOW_SPLASH_SCREEN" is the key and true is the initial value.

However, AppStorage has two main caveats. For every usage of the same key/value, you have to make sure to always use the same key and initial value. This makes it tedious when changing either one.

The Solution

We can extend AppStorage to use key path syntax, similar to how EnvironmentKeys work:

@Environment(\.dismiss) var dismiss

This way, we do not have to manually type the key, but use a predefined variable. And, we do not set the initial value at call site, making it easy to change.

First, we have to create a structure that stores the keys and values:

struct KeyValuePair<Value> {
    var key: String
    var value: Value
    
    init(_ key: String, value: Value) {…