Features I would like to see from Swift and its core ecosystem

Swift Wish List.md

Swift Wish List

Features I would like to see from Swift and its core ecosystem, to make it a robust and ergonomic language for all use cases.

• ❌ = Unimplemented
• 📜 = Manifesto
• ⚾️ = Pitch
• 💍 = Proposal
• ⛔️ = Partially Implemented / Awaiting Implementation
• ⚠️ = In Active Review
• ✅ = Accepted / Implemented
• ☑️ = Available in Latest Version (5.6)

Language Features

• 📜 Memory ownership system
• ⚾️ Variadic generics
• 💍 Flexible memberwise initialization (rationale for initial rejection)

Concurrency

• ☑️ async/await
• ☑️ async let structured concurrency bindings
• ☑️ Actors
  • ☑️ Global actors
  • ✅ Distributed actors
• ☑️ async program entry points
• ✅ Concurrency in top-level code
• ☑️ AsyncSequence
  • ☑️ AsyncStream
• ☑️ Effectful properties (async and throws)

Protocols, Existentials, & Generics

• ✅ Existentials for protocols with Self or associated type constraints as new type definitions
• ✅ Lightweight same-type requirements for primary associated types
• Enable new primary associated type syntax in more structural positions such as directly on arguments and returns for:
  • ✅ Implicitly Opened Existentials, e.g. func isReadyForFinale(_ costume: any Costume) -> Bool
  • ❌ Existential types, e.g. func test(_: any Collection<String>)
  • ❌ Opaque types, e.g. func evenValues(in: some Collection<Int>) -> some Collection<Int>
• Enable secondary associated types to be constrained directly on arguments and returns for:
  • ❌ Existential types, e.g. func test(_: any Collection where Index == Int)
  • ❌ Opaque types, e.g. func evenValues(in: some Collection where Index == Int) -> (some Collection where Index == Int)
• ⚠️ Primary Associated Types in the Standard Library
• ⛔️ Existential types (any)
• ☑️ Opaque types (some)
• ⚾ Extend existential types to allow protocol self-conformance
• ⚾️ Extend metatypes with the new meta keyword
• ❌ Allow some/any to be used with generic types, e.g. let array: any Array = [1, 2, 3]
• ❌ Allow some/any to be used with class inheritence hierarchies, e.g. let opaqueView: some UIView = MyView()

Strings

• ✅ Regex Type
• ⚠️ Regex builder DSL
• ⚠️ Regex syntax
• ⚠️ Regex literals
• 💍 More ergonomic indexing and slicing

Optionals

• ❌ Optional chaining operator (?) in orthogonal positions
• ❌ if let with any pattern match, not just optional unwraps
• ✅ Concise syntax for duplicate identifiers in if let bindings

Domain Specific Languages

• ☑️ Result builders
• ☑️ Implicit memberwise initializer
• ❌ Result builder protocol
• ☑️ Result builder let declarations
• ❌ Stateful result builders
• ❌ Virtualized ASTs (to convert native for-in loops to specialized types, like SwiftUI.ForEach)

Metaprogramming & Reflection

• ☑️ Property wrappers
• ❌ More ergonomic Codable customization
• ❌ First-class macro system
  • ❌ Pattern-matching macros, based on the aforementioned regular expression literals
  • ❌ Procedural macros
    • Based on SwiftSyntax and Mirror
    • Including its own result builder DSL
    • Definable @Attributes, so the macro can be applied to various definitions
  • ⚾️ A way to define default protocol implementations as a macro (with the ability to define helper @Attributes)
• ⚾️ Dynamic property iteration using key paths
• ⚾️ Tuple and enum key paths
• ❌ Dependent types
• ❌ Ability to assert that all properties on a type conforming to a protocol must also conform to that protocol (as Codable does)

Modules

• ❌ Namespaces
• ⚾️ Fully qualified name syntax
• ⚾️ Formalized @exported attribute

Interoperability & Platform Support

• 📜 C++ interoperability
• ❌ Rust interoperability
• ❌ COM and WinRT interoperability
• ⚾️ Formalized generic external declarations (e.g. @decl)
• ❌ Upstream WebAssembly support

Ecosystem Features

• ❌ Official Swift-only testing library
• ⚾️ Formatted command line test output
• ⚾️ Toolchain manager
• ✅ Official HTML documentation generation tool

Standard Library & Foundation

• ✅ New Clock, Instant, and Duration time types for the Standard Library
• ⛔️ Open source Foundation implementation
• ❌ Replace Foundation with modern APIs, split into individually importable submodules

Swift Package Manager

• ⚾️ Support for scripting
• ⚾️ Dynamic loading API
• ✅ Package editor commands
• ❌ Official package index
• ❌ Type-safe access to individual resource files
• ⚾️ Package features
• ☑️ Extensible build tools (and additional package plugin APIs)
• ☑️ Package Manager Command Plugins for swift package
• ⛔ Extensible Product types (added as a private API for Swift Playgrounds 4 app projects in Xcode 13.2 beta)
• ❌ Package @Attributes
• ⚾️ Manifest API based on Result Builders

SwiftNIO

• ✅ async/await support
• ❌ QUIC and HTTP/3 support