What’s new in swift 4.2?

What’s new in swift4.2?

WWDC18

Source Compatibility:One Compiler with Three Modes

Source Compatibility

Swift 3:Accepts Swift 3 code that built with Xcode 8
Swift 4:Accepts Swift 4 code that built with Xcode 9.3
Swift 4.2: Same as with Swift 4 but incorporates new Swift-related SDK. improvements

Faster Swift DebugBuilds

Swift Debug Builds
Build speeds of Xcode 10 compared to Xcode 9

swift debugbuilds

Compilation Mode versus Optimization Level

compilation maode

Stop Using Debug with Whole Module Compilation

Module compilation

UsingWhole ModuleforDebugbuilds was a stopgap to improve buildsWhole Moduleprevents incremental builds
UseIncrementalfor Debug builds!

Runtime Optimizations

// Calling Convention: “Owned” (+1 retain)class X { … }func caller() {// ‘x’ created with +1 reference countlet x = X()}foo(x)func foo(x: X) {let y = x.value// Calling Convention: “Owned” (+1 retain)class X { ... }func caller() {// ‘x’ created with +1 reference countlet x = X()foo(x)}func foo(x: X) {let y = x.value...// release x}

Collection of EnumCases

// SE-0194 Derived Collection of Enum Casesenum Gait {  case walk  case trot  case canter   case gallop  case jog  static var allCases: [Gait] = [.walk, .trot, .canter, .gallop]}for gait in Gait.allCases {  //This code will never print “jog”!  print(gait)}// SE-0194 Derived Collection of Enum Cases with using CaseIterableenum Gait: CaseIterable {  case walk  case trot  case canter   case gallop  case jog}for gait in Gait.allCases {  print(gait) // It will print all cases}

Conditional Conformance

Inconsistent Behavior in Swift 4.0

Why Aren’t All Arrays Equatable?

Conditional Conformance

Conditional Conformance Allows Composition

Synthesized Equatable and Hashable

// SE-0185 Synthesizing Equatable and Hashable Conformancestruct Restaurant: Equatable {    let name: String   let hasTableService: Bool   let kidFriendly: Bool}// SE-0185 Synthesizing Equatable and Hashable Conformancestruct Restaurant: Hashable {    let name: String   let hasTableService: Bool   let kidFriendly: Bool}// Synthesizing Conditional Equatable and Hashableenum Either<Left, Right> {    case left(Left)   case right(Right)}extension Either: Equatable where Left: Equatable, Right: Equatable { }extension Either: Hashable where Left: Hashable, Right: Hashable { }// This just works!var mySet = Set<Either<Int, String>>()