Use-cases for Swift interop in .NET 10

[kotlarmilos]

Overview

This issue presents use-cases we want to support. They are required to define and limit the scope of Swift interop effort in .NET 10. While it's difficult to clearly specify the exact Swift language features that will be supported in the next release, we can establish our definition of done.

Milestone 1 – StoreKit2 purchase MVP

Implement basic purchase functionality without UI components. Below is an example of Swift pseudo code.

func requestProducts() async {
    do {
        let storeProducts = try await Product.products(for: productIdentifiers)
        products = storeProducts
    } catch {
        print("Error fetching products: \(error)")
    }
}

func purchase(_ product: Product) async throws -> Transaction? {
    let result = try await product.purchase()
    return result
}

Objectives

• Establish projection tooling skeleton: parsers->marshalers->emitters
• Project structs and it's members
• Project Swift runtime features: metadata, value witness table, and async
• Project optional types
• Project Swift errors/exceptions in C#
• Project StoreKit2 types with its members needed for the basic purchase functionality. Specifically:
  • struct Product : Swift.Identifiable {}
  • struct Transaction : Swift.Identifiable {}

Deliverables

• [Projection tooling] Implement type database runtimelab#2842
• [Swift runtime features] Implement Swift metadata runtimelab#2838
• [Swift runtime features] Implement Swift value witness tables support runtimelab#2840
• [Swift runtime features] Implement Swift errors in C# runtimelab#2928
• [Swift language features] Implement Swift structs in C# runtimelab#2822
• [Swift language features] Implement Swift async runtimelab#2837
• [Swift language features] Implement Swift.Optional in C# runtimelab#2929
• [Swift shipping] Add tooling sorting modules in topological order for processing runtimelab#2913
• [Swift shipping] Add debugging experience for projection tooling/ binding generation runtimelab#2902

Risks

• Work items are too broad, which may affect group focus
• Significant fundamental work on the projection tooling in a single iteration

Milestone 2 – Subscriptions and list purchased products

Implement advanced purchase experience with subscriptions and list of already purchased products. Below is an example of Swift pseudo code.

func updateProductStatus() async {
    var purchasedProducts: [Product] = []

    for await result in Transaction.currentEntitlements {
        do {
            switch transaction.productType {
            case .nonConsumable:
                //
            case .nonRenewable:
                // 
            case .autoRenewable:
                // 
            default:
                break
            }
        } catch {
            print("Transaction failed verification: \(error)")
        }
    }
}

Objectives

• Project enums and it's members
• Project StoreKit2 types needed for subscriptions purchase functionality. Specifically:
  • struct Transaction : Swift.Identifiable {}
  • struct SubscriptionPeriod : Swift.Equatable, Swift.Hashable {}
  • struct SubscriptionOffer : Swift.Equatable, Swift.Hashable {}
  • struct RenewalState : Swift.RawRepresentable, Swift.Equatable, Swift.Hashable {}
  • struct RenewalInfo {}
  • struct ExpirationReason : Swift.RawRepresentable, Swift.Equatable, Swift.Hashable {}
  • struct SubscriptionInfo : Swift.Equatable, Swift.Hashable {}
  • enum StoreKitError : Swift.Error {}
  • enum PurchaseResult {}
  • enum VerificationResult<SignedType> {}

Deliverables

• [Swift language features] Implement Swift enums in C# runtimelab#2823
• [Swift language features] Implement Swift generics support for structs runtimelab#2930
• [Swift language features] Implement Swift generics support for enums runtimelab#2931
• [Swift language features] Implement Swift.Set in C# runtimelab#2834
• [Swift language features] Implement Any / Some in C# runtimelab#2835
• [Swift language features] Implement Swift.Set in C# runtimelab#2834
• [Swift language features] Implement Swift.Array in C# runtimelab#2833
• [Swift language features] Implement Foundation.String in C# runtimelab#2831
• [Projection tooling] Add symbols from dynamic library to type database runtimelab#2918

Risks

• Limited functionality due to dependencies on other frameworks

Milestone 3 – Pack StoreKit2 bindings in the experimental NuGet

Pack and distribute StoreKit2 bindings for supported scenarios.

Objectives

• Distribute StoreKit2 bindings
• Lock the design of projection tooling input: ABI parser and MacO reader
• Learn limitations of the bindings

Deliverables

• [Projection tooling] Lock the design of projection tooling input: Implement ABI and MachO parser runtimelab#2845
• [Swift shipping] Implement tooling/bindings distribution using NuGet packages runtimelab#2849
• [Swift shipping] Implement testing framework runtimelab#2850
• [Swift shipping] Add end-to-end tests for the StoreKit2 framework runtimelab#2932

Risks

• Limited functionality due to dependencies on other frameworks
• Incomplete / non-functional bindings
• Poor UX

This is the first end-to-end milestone. All following milestones are informational/ tentative only, and will be updated according to the progress.

Milestone 4 – Basic SwiftUI controls

Integrate native SwiftUI controls into a MAUI-based app. Below is an example of Swift pseudo code.

 public func getTextView() -> UIView {
     let swiftUIView = Text("Hello from Swift!").font(.title)
     let hostingController = UIHostingController(rootView: swiftUIView)
     return hostingController.view
}

Objectives

• Project SwiftUI types needed for a simple UI example. Specifically:
  • struct Text {}
  • struct Button<Label> where Label : View {}
  • struct Label<Title, Icon> where Title : View, Icon : View {}
  • struct Image {}
  • class UIHostingController<Content> where Content : View

Deliverables

• [Swift language features] Implement Swift protocols in C# runtimelab#2824
• [Swift runtime features] Implement Swift existential containers runtimelab#2841

Milestone 5 – Support StoreKit2 views using SwiftUI

Integrate advanced SwiftUI views into MAUI-based app.

Objectives

• Project StoreKit2 views for improved UX. Specifically:
  • struct ProductView {}
  • struct StoreView {}
  • struct SubscriptionStoreView {}

Deliverables

• [Swift language features] Implement Swift closures in C# runtimelab#2828
• [Swift language features] Implement Swift tuples in C# runtimelab#2933
• [Swift language features] Implement Swift classes/ actors in C# runtimelab#2934

Milestone 6 – Pack SwiftUI in the experimental NuGet

Pack and distribute SwiftUI bindings for supported scenarios.

Objectives

• Distribute SwiftUI bindings
• Lock the design of projection tooling output: string-based and model-based emitters
• Learn limitations of the bindings

Deliverables

• [Swift ABI compatibility] Implement memory ownership between Swift and C# bindings runtimelab#2851
• [Projection tooling] Lock the design of projection tooling output: Implement string-based and model-based emitters runtimelab#2843
• [Swift language features] Improve UX of generated bindings runtimelab#2935
• [Swift language features] Implement common interfaces in projections (IEnumerable, ICollection, IDisposable) runtimelab#2829
• [Swift shipping] Add end-to-end tests for the SwiftUI framework runtimelab#2936

Milestone 7 – Test all the frameworks from the SDK

Objectives

• Run the tooling on all SDK frameworks to test coverage
• Distribute the projection tooling

Deliverables

• [Projection tooling] Lock the overall design of the projection tooling runtimelab#2846
• [Swift shipping] Performance benchmarking framework for Swift projection tooling runtimelab#2586

Milestone 8 - Deploy the Hiking app

Deploy experimental .NET iOS app which demonstrate the capabilities of the nSwift interop.

Objectives

• Implement in-app purchase
• Implement authentication feature using the built-in SignInWithAppleButton
• Integrate native SwiftUI controls into MAUI-based applications

Note

The .NET iOS app with generated bindings will be experimental in .NET 10 and will not be officially supported.

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Issue Details

---

Description

This issue tracks the top-level scenarios for end-users regarding .NET Swift interop. The goal is to demonstrate the practical application of .NET Swift interop within Maui scenarios. One possible approach is to select an existing Maui sample from https://github.com/dotnet/maui-samples and improve it by incorporating native libraries and widgets, such as UIKit or SwiftUI. There are some other ideas, which may be desirable but not required, and will be added later.

Below is a list of tasks that needs to be implemented. Please note that the breakdown of the issues does not impose hard deadlines. If some of the functionality does not get upstreamed for a particular preview version, this issue will be updated accordingly.

Tasks

.NET9 Preview 1

• Compile a list of libraries and features to support in .NET 9
• Select Maui applications to showcase the .NET Swift interop
• Propose design for VSCode extension

.NET9 Preview 2

• Update Maui applications to utilize the .NET Swift interop
• Implement and deploy the VSCode extension

.NET9 Preview 3

• Implement telemetry for BTfS usage
• Write a blog post that showcases the usage of .NET Swift interop

.NET9 Preview 4

TBD

Author:	kotlarmilos
Assignees:	kotlarmilos
Labels:	area-Meta, User Story
Milestone:	9.0.0

[clarky07]

I think live activity support would make sense for this (and lots of other use cases). Just commenting here as a suggestion I got from another issue.

[kotlarmilos]

Thanks, there is a tracking issue: xamarin/xamarin-macios#17038

[amirvenus]

There are also some libraries available in Swift such as Apple's MLX.

It would be great if one could easily interop into Swift from .net.

[kotlarmilos]

There are also some libraries available in Swift such as Apple's MLX.

Created a tracking issue: xamarin/xamarin-macios#21811