AppCodableStorage

Extends @AppStorage in SwiftUI to support any Codable object. I use SwiftUI for quick prototypes, and this makes it a lot easier to stay organized.

Just swap @AppCodableStorage for @AppStorage and tag your type as PropertyListRepresentable and you're good to go.

Like AppStorage

struct Config: PropertyListRepresentable {
    var username: String
    var profileColor: NSColor?
}

struct MyView: View {

  @AppCodableStorage("user") var settings = Config(username: "Steve")
    
  var body: some View {
    TextField($config.username)
    ...
  }
}

Supported

Use storage in multiple views, they automatically reflect the most recent value
projectedValue / Bindings so you can pass a sub-object into a sub-view mutably
Observes UserDefaults so it can interoperate with other code / defaults write … changes

Outside of SwiftUI

The underlying implementation is in DefaultsWriter, which is useful if you have other subsystems in your app that want to write to and observe UserDefaults in this way. For that purpose, there is also a DefaultsWriter.objectDidChange Publisher to use when you want the updated value rather than a signal that it's about to change.

Limitations

Root must code as a Dictionary
Encodes to Data and back

The default implementation of PlistReprestable is inelegant, but supports the same use cases as PlistEncoder, since I use PlistEncoder to first convert to Data and then decode the data.

A "better" solution would be to copy-paste most of the code from PlistEncoder to be able to use PlistCoder.encodeToTopLevelContainer(), which is marked internal in the standard library. If it were made public, this could be much more elegant.

Alternates considered

You can use RawRepresentable with the built-in AppStorage to store Codable in a string key in UserDefaults`. This means that your defaults is now unreadable since there is a weird string or binary data in there.

I realize Mike Ash independently made TSUD, which does something pretty similar prior to SwiftUI.

Warning

Do not use this to store a large amount of data! No images, unlimited amounts of text, files etc.