What’s New in Swift 4.2?

Miscellaneous Bits and Pieces

There are a few other changes in Swift 4.2 you should know about:

Swift Package Manager Updates

Swift 4.2 adds a few improvements to the Swift Package Manager:

Defining Swift language versions for packages

Swift 4.1 defined swiftLanguageVersions in Package.swift as [Int], so you could declare only major releases for your packages:

let package = Package(name: "Package", swiftLanguageVersions: [4])

Swift 4.2 lets you define minor versions as well with SwiftVersion cases [SE-0209]:

let package = Package(name: "Package", swiftLanguageVersions: [.v4_2])

You can also use .version(_:) to declare future releases:

let package = Package(name: "Package", swiftLanguageVersions: [.version("5")])

Declaring local dependencies for packages

In Swift 4.1, you declared dependencies for your packages using repository links. This added overhead if you had interconnected packages, so Swift 4.2 uses local paths in this case instead [SE-0201].

Adding system library targets to packages

System-module packages required separate repositories in Swift 4.1. This made the package manager harder to use, so Swift 4.2 replaces them with system library targets [SE-0208].

Removing Implicitly Unwrapped Optionals

In Swift 4.1, you could use implicitly unwrapped optionals in nested types:

let favoriteNumbers: [Int!] = [10, nil, 7, nil]
let favoriteSongs: [String: [String]!] = ["Cosmin": ["Nothing Else Matters", "Stairway to Heaven"], 
                                          "Oana": nil] 
let credentials: (usermame: String!, password: String!) = ("Cosmin", nil)

Swift 4.2 removes them from arrays, dictionaries and tuples [SE-0054]:

let favoriteNumbers: [Int?] = [10, nil, 7, nil]
let favoriteSongs: [String: [String]?] = ["Cosmin": ["Nothing Else Matters", "Stairway to Heaven"], 
                                          "Oana": nil] 
let credentials: (usermame: String?, password: String?) = ("Cosmin", nil)

Where to Go From Here?

You can download the final playground using the Download Materials link at either the top or bottom of this tutorial.

Swift 4.2 improves upon many Swift 4.1 features and prepares the language for ABI stability in Swift 5, coming in early 2019.

You can read more about the changes in this version either on the official Swift CHANGELOG or the Swift standard library diffs.

You can also check out the Swift Evolution proposals to see what changes are coming in Swift 5. Here you can give feedback for current proposals under review and even pitch a proposal yourself!

What do you like or dislike about Swift 4.2 so far? Let us know in the forum discussion below!