Written by Ramit Sharma

Description: Learn how you can use Swift in your C++ and Objective-C++ projects to make your code safer, faster, and easier to develop. We'll show you how to use C++ and Swift APIs to incrementally incorporate Swift into your app.

Basics of interoperability

Incremental adoption

• Builds on Objective-C interoperability
  • Supports incremental Swift adoption

Using Swift in more places

• Adopt Swift in large C++ codebases.
  • Use C++ libraries in Swift.
  • Remove Objective-C bridging.
  • While using C++ frameworks, Xcode imports C++ APIs automatically and don’t need a bridging header.
  • Enable C++ interoperability in the build settings.

  // Calling a C++ method from Swift
  func loadImage(_ image: UIImage) {
  // Load an image into the shared C++ class.
  CxxImageEngine.shared.pointee.loadImage(image)
}

  // importing a C++ framework 
  import CxxImageKit

Bidirectional interoperability

• Incremental Swift adoption.
  • Completely automatic integration by the Swift compiler without writting a Bridging layer.
  • Direct calls and no overheads when calling APIs in Swift and vice-versa.
  • C++ APIs availablity in Swift:
    • can import most C++ collections, both from the standard library and elsewhere
      • Collections: std::vector, std::map, User-defined
    • handlew function templates and class template specializations
    • supports managing memory using shared pointer and similar user-defined types.
      • Smart pointers: std::shared_ptr, user-defined
    • Members: methods, properties and intializers
    • Generics: structs and enums
    • Standard library: swift::Array, swift::String, and swift::Optional
    • Library evolution: resilient structs and classes

• Xcode Compatiblity
  • Code completion
  • Jump-to-definition
  • Global rename
  • Debugger support

Natural Swift APIs

• Swift compiler is able to automatically import most C++ APIs and represent them as safe Swift APIs.
  • Getters and Setters -> Methods
  • Value types -> Structs
  • Reference Types -> Pointers
  • Operators -> Operators
  • Containers -> Swift Collections
  • Constructors -> initializers
  • Swift compiler allows us to fine-tune how APIs are imported and expose APIs that feel even more natural by providing the compiler with more information about your APIs through the use of annotations.
  • structs represent value types and classes represent reference types.
  • C++ types will be imported as value types in Swift.

Imported value types

• Short lifetimes and deep copies.
  • Copy constructor and destructor manage lifetime.

Collections

• Imports any type with begin and end methods as Swift collection.
  • Swift Collections can be used in for-loops, map, filter

Swift Collections Safety

• use these Swift Collection APIs rather than C++ iterator APIs which do not fit into Swift's safety model.
  • The Swift compiler will help guide you towards these safer APIs by marking unsafe C++ APIs as unavailable and suggesting a safer alternative.
  • C++ doesn't have a strong distinction between value types and reference types.
  • Swift also gives you the option to import some things as reference or class types by adding an annotation to your C++ code.

Foreign reference types

• map CxxImageEngine to a Swift class using the SWIFT_SHARED_REFERENCE attribute.
  • Enforces reference sematics.
  • Removes UnsafePointer indirection.
  • Manages lifetime with custom retain and release operations.

  //importing swift/bridging
  #import <swift/bridging>

  //Applying SWIFT_SHARED_REFERENCE attribute to CxxImageEngine
  struct SWIFT_SHARED_REFERENCE(IKRetain, IKRelease) CxxImageEngine {
      // ...
  };

Computed properties

SWIFT_COMPUTED_PROPERTY attribute maps getter and setter to property.

   /// \returns all images that have been loaded into the engine. Includes any modifications that were
   /// applied to the images.
   SWIFT_COMPUTED_PROPERTY
   inline std::vector<Image *_Nonnull> getImages() const;

Future evolution

• Evolve based on your feedback.
  • Opt-in to changes with interoperability versions.
  • You can join the workgroup and get involved on the forums. Just head to Mixing Swift and C++