Kuba Suder's blog on Mac & iOS development

What's new in Swift

Categories: Swift, WWDC 20 0 comments Watch the video

Improvements to binary size, especially in SwiftUI apps

Smaller memory usage overhead from things like internal caches of the Swift runtime (use iOS 14 deployment target for best effect)

Apple can now use Swift in very low level frameworks, where previously only C was available

Much better compiler diagnostics (warnings and errors)

New diagnostics subsystem that helps identifying code issues much more precisely

More actionable errors with guidance how to fix them

Improved code completion

Code completion better understands features such as ternary operator or keypaths

Drastically improved performance, up to 15x faster

Improved code indentation in things like: chained calls, call arguments, multi-line control flow statements

Better error messages for runtime failures like arithmetic overflow

Debugging improvements: improved module importing which should lead to less issues while evaluating variables in lldb

Cross-platform support:

Improved support for various distributions of Linux

Coming soon: initial support for Windows

Swift AWS Lambda runtime

New language features:

Multiple trailing closures

(API design tip: design names for methods with closure arguments so that the call site still makes sense if a trailing closure w/o an argument label is used)

Keypaths can be used as functions, so you can pass them to APIs that expect a function, like\.field) (this is from Xcode 11.4)

@main – marks the entry point to the program

As a library author, you can declare a static function main() in a class or type

Users can then use an instance of that type with the tag @main, and compiler implicitly creates a main.swift file that calls that function

class Foo {
  public static func main() {
import FooKit

class Hello: Foo {

Replaces the old @UIApplicationDelegate which could only be used in the specific context of UIApplicationDelegate

Increased availability of implicit self in closures:

  • you can skip self. if you capture [self] in the closure arguments
  • you can skip self. if self is a struct or enum (like in SwiftUI)

Multi-clause catch statements in do-catch

Automatic comparable conformance for (some) enum types

Enums can fulfill protocol requirements requiring static properties (plain case) and static functions (case with arguments)

View builders improvements:

  • support for more kinds of statements, e.g. switch and if-let
  • adding a view builder annotation to body declaration if it has more than one children is not necessary anymore

Float16 – a float type that uses 2 bytes (half of standard float)

Apple Archive – new archive file format, .aar extension

Fast, uses multithreading

Includes a command-line tool and Finder integration

Swift API – AppleArchive framework

Swift System – Swift interfaces to system calls and other low level APIs


Improved performance

Support for string interpolations and formatting options:

logger.log("\(offerID, align: .left(columns: 10), privacy: .public)")
logger.log("\(seconds, format: .fixed(precision: 2)) seconds")

Packages available on GitHub:

Swift Numerics

Swift Argument Parser

Swift Standard Library Preview