What’s new in Swift

Summary

• Swift 6.3 and 6.4 bring significant language and library improvements, enhancing developer efficiency and code safety.

• New tools for task cancellation, file path manipulation, and API deprecation handling improve code management.

• Performance tuning features in Swift simplify optimizing code without sacrificing safety.

• Enhanced interoperability and new SDKs expand Swift’s usability across platforms like Android and web apps.

• Swift’s ownership system and new APIs make high-performance programming safer and more accessible.

Presenters

• Becca, Swift Team

• Evan, Swift Team

Language Improvements

• Optional Handling: Swift 6.4 removes the need for parentheses with some or any and optional types.

• Error Handling: Warnings for unhandled errors in concurrency tasks.

• Async Functions: Now callable from a defer block.

• Sendable Checking: weak let supports immutability, and ~Sendable syntax for non-sendable types (doesn’t stop subclasses from being Sendable).

• Initializer Enhancements: Structs with mixed visibility properties get a second member-wise initializer.

   struct Briefing {
      internal var topic: String
      internal var scheduledAt: Date
      private  var attendees: [Person] = []
   }
  
   // Generated memberwise initializers:
   // extension Briefing {
   //     private init(topic: String, scheduledAt: Date, attendees: [Person] = []) { 
   //          self.topic = topic
   //          self.scheduledAt = scheduledAt
   //          self.attendees = attendees
   //     }
   // 
   //     internal init(topic: String, scheduledAt: Date) {
   //          self.topic = topic
   //          self.scheduledAt = scheduledAt
   //          self.attendees = []
   //     }
   // }

• Cross-Platform Availability: anyAppleOS condenses platform names for OS availability attributes (only supported for OSes 26 and newer).

  extension Mission {
     @available(anyAppleOS 27, *)
     func showStatus() { ... }
  
     @available(anyAppleOS 27, *)
     @available(tvOS, unavailable)
     func launch() { ... }
  
     #if os(anyAppleOS)
     func makeLiveActivityWidget() -> some Widget { ... }
     #endif
  }

• Deprecated APIs: @diagnose attribute can manage warnings for deprecated APIs.

   @diagnose(DeprecatedDeclaration, as: ignored, reason: "Flying with surplus hardware")
   func makeApolloSoyuzMission() -> Mission {
      CrewedMission(
         rocket: makeSaturnIRocket(),
         payload: makeApolloCSM(),
         crew: [.daniellePoole, .nathanMorrison]
      )
   }
  
   @diagnose(StrictMemorySafety, as: warning)
   func uplinkCommand(from receiver: inout Receiver, to computer: inout Computer) {
      let commandSize = receiver.receiveInt()
      receiver.withReceivedData(byteCount: commandSize) {
         computer.receiveUplinkedCommand($0)
      }
   }
  
   @diagnose(ErrorInFutureSwiftVersion, as: error)
   func fetchPosition() -> (x: Double, y: Double, z: Double) {
      return self.rotation
   }

• Module Selectors: New :: syntax disambiguates which module a declaration comes from.

   import Rocket
   import GiftShopToys
  
   let rocket1 = SaturnV()            // could mean `Rocket::SaturnV` or `GiftShopToys::SaturnV`
   let rocket2 = Rocket.SaturnV()     // prefers `Rocket::Rocket.SaturnV`
   let rocket3 = Rocket::SaturnV()    // correctly finds `Rocket::SaturnV`

Library Updates

• Standard Library: New tools for task cancellation, dictionary transformations, and file paths.

   // Radio for help
  
   extension Radio {
      func send(_ data: [UInt8]) {
         if Task.isCancelled { return }
         // ...
      }
   }
  
   extension EmergencyTransponder {
      func sendSOS() {
         withTaskCancellationShield {
            radio.send(makeSOSPacket())
         }
      }
   }

   // Map values with keys
  
   func makeCalendarDisplayNames(for missions: [Mission: LaunchWindow]) -> [Mission: String] {
      missions.mapKeyedValues { mission, launchWindow in
         makeDisplayName(for: mission, in: launchWindow)
      }
   }

   // FilePath handling macOS-named resources
  
   var path: FilePath = "/var/www/static"
   path.components.append("WWDC")
   print(path.components)
   // [ "var", "www", "static", "WWDC" ]
  
   var path: FilePath = "/var/www/static/..namedresource/rsrc"
   print(path.components)
   // [ "var", "www", "static" ]

• Swift Testing: Enhanced control over test behavior, including non-fatal issues, dynamic test cancellation, and new swift test options --maximum-repetitions and --repeat-unit.

  // Issue severity
  
  @Test(arguments: allRockets)
  func testBurn(rocket: Rocket) throws {
     rocket.burn(for: .seconds(150))
     let remaining = rocket.propellantKg / rocket.totalPropellantKg
  
     if remaining < 0.10 {
        Issue.record(
              "\(rocket.name) remaining fuel is below 10% reserve target",
              severity: .warning
        )
     }
  
     #expect(remaining > 0.02, "\(rocket.name) propellant critically low - abort")
  }

  // Test Cancellation
  
  @Test(arguments: allRockets)
  func testBurn(rocket: Rocket) throws {
     // solid-fuel rocket engines can't be stopped
     if rocket.engineType == .solid {
        try Test.cancel("\(rocket.name) has solid fuel")
     }
  
     rocket.burn(for: .seconds(150))
     let remaining = rocket.propellantKg / rocket.totalPropellantKg
  
     if remaining < 0.10 {
        Issue.record(
              "\(rocket.name) remaining fuel is below 10% reserve target",
              severity: .warning
        )
     }
  
     #expect(remaining > 0.02, "\(rocket.name) propellant critically low - abort")
  }

• Subprocess Package: Refined APIs with improved error handling and cross-platform support.

  // Subprocess output streaming
  
  let result = try await Subprocess.run(.name("ls"),
                                        input: .none,
                                        output: .sequence,
                                        error: .string(limit:4096)) { execution in
        execution.standardOtput.strings().filter { $0.hasSuffix(".obj") }
  }
  
  for try await objectFiles in result.closureOutput {
     print("Object file: \(objectFile)")
  }

• Foundation Enhancements: Progress manager for async/await, faster data operations, and unification of URL types.

   // Progress reporting
  
   let manager = ProgressManager(totalCount: 100)
   try await rocket.launch(mission.subprogress(assigningCount: 100))
  
   extension Rocket {
      func launch(_ progress: consuming Subprogress? = nil) async throws {
         let stage = progress?.start(totalCount: 3)
         try await ignite(); stage?.complete(count: 1)
         try await liftoff(); stage?.complete(count: 1)
         try await stageSeparation(); stage?.complete(count: 1)
      }
   }

Performance Tuning

• Optimizer Control: New inline(always) attribute and @specialized for fine-tuning optimization.

  @inline(never) // or @inline(always)
  func makeInts(randomized: Bool) -> [256 of Int] {
     if randomized {
        InlineArray { _ in Int.random(in: (.min)...(.max)) }
     } else {
        InlineArray(repeating: 0)
     }
  }

  @specialized(where Values == [UInt8])
  func histogram<Values>(of values: Values) -> [256 of Int] where Values: Sequence<UInt8> {
     var result = makeInts(randomized: false)
  
     for value in values {
        result[Int(value)] += 1
     }
  
     return result
  }

• Ownership System: Enhancements allow non-copyable types and improved handling of Equatable and Comparable.

• Iterables: New Iterable protocol for more efficient loops.

• Accessors: borrow and mutate accessors replace get and set for performance gains.

   @safe public struct UniqueBox<Value: ~Copyable>: ~Copyable {
      private let valuePointer: UnsafeMutablePointer<Value>
  
      public init(_ value: consuming Value) {
         valuePointer = UnsafeMutablePointer.allocate(capacity: 1)
         valuePointer.initialize(to: value)
      }
  
      public var value: Value {
         borrow { valuePointer.pointee }
         mutate { &valuePointer.pointee }
      }
  
      deinit {
         valuePointer.deinitialize(count: 1)
         valuePointer.deallocate()
      }
   }

• New Safe APIs: UniqueBox and UniqueArray for managing pointers and non-copyable elements; Ref / MutableRef — like a Span but for one value; storable, passable, returnable, usable in generics.

Cross-Platform and Interoperability

• Exposing Swift to C: New @c attribute for exposing Swift functions to C.

• Java Interop: Async and throwing Swift functions are now callable from Java.

• Android SDK: Official Swift SDK for Android released.

• Swift Extension for VS Code: Tools for easy toolchain management and WebAssembly support.

• JavaScript Interop: Safer and faster bridging with JavaScript kit improvements.

• Embedded Swift: Now supports existential types and untyped throws.

The Future of Swift

• Swift Build is now the default build-system backend for Swift Package Manager, for consistency between SwiftPM and Xcode builds.