Instantly share state among your app's features and external persistence layers, including user defaults, the file system, and more.
This library was motivated and designed over the course of many episodes on Point-Free, a video series exploring functional programming and the Swift language, hosted by Brandon Williams and Stephen Celis.
This library comes with a few tools that allow one to share state with multiple parts of your
application, as well as external systems such as user defaults, the file system, and more. The tool
works in a variety of contexts, such as SwiftUI views, @Observable models, and UIKit view
controllers, and it is completely unit testable.
As a simple example, you can have two different observable models hold onto a collection of data that is also synchronized to the file system:
// MeetingsList.swift
@Observable
class MeetingsListModel {
@ObservationIgnored
@Shared(.fileStorage(.meetingsURL)) var meetings: [Meeting] = []
}
// ArchivedMeetings.swift
@Observable
class ArchivedMeetingsModel {
@ObservationIgnored
@Shared(.fileStorage(.meetingsURL)) var meetings: [Meeting] = []
}Note
Due to the fact that Swift macros do not play nicely with property wrappers, you must annotate
each @Shared held by an @Observable model with @ObservationIgnored. Views will still update
when shared state changes since @Shared handles its own observation.
If either model makes a change to meetings, the other model will instantly see those changes.
And further, if the file on disk changes from an external write, both instances of @Shared will
also update to hold the freshest data.
The @Shared property wrapper gives you a succinct and consistent way to persist
any kind of data in your application. The library comes with 3 strategies:
appStorage,
fileStorage, and
inMemory.
The appStorage strategy is useful for store small pieces of simple data
in user defaults, such as settings:
@Shared(.appStorage("soundsOn")) var soundsOn = true
@Shared(.appStorage("hapticsOn")) var hapticsOn = true
@Shared(.appStorage("userSort")) var userSort = UserSort.nameThe fileStorage strategy is useful for persisting more complex data
types to the file system by serializing the data to bytes:
@Shared(.fileStorage(.meetingsURL)) var meetings: [Meeting] = []And the inMemory strategy is useful for sharing any kind of data globally
with the entire app, but it will be reset the next time the app is relaunched:
@Shared(.inMemory("events")) var events: [String] = []See "Persistence strategies" for more information on leveraging the persistence strategies that come with the library, as well as creating your own strategies.
It is possible to use @Shared state essentially anywhere, including observable models, SwiftUI
views, UIKit view controllers, and more. For example, if you have a simple view that needs access
to some shared state but does not need the full power of an observable model, then you can use
@Shared directly in the view:
struct DebugMeetingsView: View {
@Shared(.fileStorage(.meetingsURL)) var meetings: [Meeting] = []
var body: some View {
ForEach(meetings) { meeting in
Text(meeting.title)
}
}
}Similarly, if you need to use UIKit for a particular feature or have a legacy feature that can't use
SwiftUI yet, then you can use @Shared directly in a view controller:
final class DebugMeetingsViewController: UIViewController {
@Shared(.fileStorage(.meetingsURL)) var meetings: [Meeting] = []
// ...
}And to observe changes to meetings so that you can update the UI you can either use the
Shared/publisher property or the observe tool from our Swift Navigation
library. See "Observing changes" for more information.
Features using the @Shared property wrapper remain testable even though they interact with outside
storage systems, such as user defaults and the file system. This is possible because each test gets
a fresh storage system that is quarantined to only that test, and so any changes made to it will
only be seen by that test.
See "Testing" for more information on how to test your features when using @Shared.
The documentation for releases and main are available here:
- Shared
- Persistence strategies
- Mutating shared state
- Observing changes to shared state
- Deriving shared state
- Reusable, type-safe keys
- Initialization rules
- Testing
- Gotchas
This repo comes with lots of examples to demonstrate how to solve common and complex problems with Sharing. Check out this directory to see them all, including:
-
Case Studies: A number of case studies demonstrating the built-in features of the library.
-
FirebaseDemo: A demo showing how shared state can be powered by a remote Firebase config.
-
GRDBDemo: A demo showing how shared state can be powered by SQLite in much the same way a view can be powered by SwiftData's
@Queryproperty wrapper using GRDB. -
WasmDemo: A SwiftWasm application that uses this library to share state with your web browser's local storage.
-
SyncUps: We also rebuilt Apple's Scrumdinger demo application using modern, best practices for SwiftUI development, including using this library to share state and persist it to the file system.
You can add Sharing to an Xcode project by adding it to your project as a package.
If you want to use Sharing in a SwiftPM project, it's as
simple as adding it to your Package.swift:
dependencies: [
.package(url: "https://github.com/pointfreeco/swift-sharing", from: "1.1.0")
]And then adding the product to any target that needs access to the library:
.product(name: "Sharing", package: "swift-sharing"),If you want to discuss this library or have a question about how to use it to solve a particular problem, there are a number of places you can discuss with fellow Point-Free enthusiasts:
-
For long-form discussions, we recommend the discussions tab of this repo.
-
For casual chat, we recommend the Point-Free Community Slack.
This library is released under the MIT license. See LICENSE for details.