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Whats_New_in_Swift.md

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WWDC 2017

Table of Contents

What's New in Swift - Tuesday

Session video and resources: https://developer.apple.com/videos/play/wwdc2017/402/

General Announcements

  • Toolchain support for more refactors in XCode
  • Swift Package Manager
    • New Manifest API

Access Control

  • Expand the scope of private needs, meaning that private flag will expose variables to the same file for extensions. No need to use fileprivate anymore

Composing Classes & Protocols

  • Usage of things like [UIControl & SomeProtocol]. Allowing to compose certain classes with certain protocols rather than trying to conform to UIControl and make them conform to SomeProtocol

Source Compatibility

  • Swift 3.2 allows Swift 3 syntax that has changed in Swift 4
  • Smoother migration to Swift 4
  • Per-target Swift compiler option Swift 3.2 or Swift 4.0

New Build System

  • Project Settings -> Shared Project Settings -> Build System -> New Build System
  • Precompiled bridging headers speed up the build process
  • Shared build for coverage testing
    • No additional build on top to generate coverage
  • Indexing while building
    • Build process now updates the index
    • Small overhead on the build time

Predictable Performance

Good to watch understanding swift performance from the last year

  • Large values are allocated in the heap and heap allocation is slow, costly
  • COW (Copy on write) optimizes large chunks of value types and allow to use same buffer if no modification is done (read only operation)
  • Stack allocation for generic buffers and unspecialized generic code

Smaller Binaries

  • Compiler level optimization for unused code pieces
  • Swift 3 automatically infers @objc if there is an instance of NSObject. This does some autogeneration for obj-c specific signatures. These methods are not detected if they are not even used.
  • @objc marking is suggested on extensions and specific functions.
  • Migrator for minimal inference
    • Migrator will mark inferred obj-c chunks as deprecated
    • Check the console for these kind of warnings (@objc)
  • Change Swift 3 @objc inference to default after your refactor and optimization is done

Symbol Size

  • Swift symbols take a lot of space
  • Symbol Stripping (reduces app size)
    • Strip Swift Symbols is Yes by default
    • View symbols with xcrun dyldinfo -- (TBD)

Strings

  • Unicode correctness by default
    • In Swift a Character is a grapheme meaning that every character is a single representation .count = 1
  • In Swift 4, strings are collection of characters
    • somestring.{} rather than somestring.characters.{}
  • String Slicing 
    let s = "one, two, three"
s.split(seperator: ",") -> ["one", "two", "three"] : [Substring]
    • Substring is a new type to avoid memory leaks. E.g: Prevent holding the whole buffer for a small part of a huge string. Wrap this into a String again after the operation is done.
  • Multi-line String Literals
    • Triple Quoted Strings """
    let test = """
          Bla
          Bla
          Bla
          """

New Generics Features

  • associatedtype extensions for protocols to avoid Iterator.element and use Element
  • Generic Subscripts

Exclusive Access to memory

  • Ownership
  • Multi-threaded Enforcement
    • Threat sanitizer cathes these errors
  • This will be a warning in Swift 3.2, will be an error in future releases

Taking Advantage of Exclusive Access

  • More reliable performance
  • Lots of optimization in libraries, compiler lvl etc.

Enforcement in the Developer Preview

  • Compile time enforcement is enabled by default