What is new in Swift 4.2 - my summary

I just have watched the What’s new in Swift from WWDC 2018 and I thought it is a great motivation to write a blog post about this talk and summarize what I learned.

And here are some new Swift 4.2 features that I really liked.

Hope you will enjoy! 🤓

SE-0194 Derived Collection of Enum Cases

In case we need to print all available enum values, we had to create some helper variable that includes all enum cases. For example, a static array called allCases. A big drawback in that approach is that we need to remember to update the allCases array every time when we modify enum cases.

Swift 4.1 approach:

enum CarType {
    case sedan
    case crossover
    case hothatch
    case muscle
    case miniVan

    static var allCases : = [.sedan, .crossover, .hothatch, .muscle, miniVan]

in Swift 4.2 we can work with CaseIterable protocol which does all the work for us! Please take a look at the below example:

// CaseIterable protocol gave us a `allCases` variable, which is an array of all cases in the Enum.

enum CarType : CaseIterable {
    case sedan
    case crossover
    case hothatch
    case muscle
    case miniVan

    //there is no need to add `allCases` variable. `CaseIterable` protocol do the job!
for type in CarType.allCases {

Conditional Conformance

let arrayOfArrays = [[1,2],[3,4],[5,6]]

arrayOfArrays.contains([1,2]) // return false in Swift 4.1

arrayOfArrays.contains([1,2]) // now it returns True because of fact that the elements in the array conforms to Equatable protocol

It will work with Optional, Dictionary types as well. The conditional conformance works in the same way with Hashable, Encodable and Decodable protocols. So for example, because Int is Hashable, which means in that case that Int? is Hashable too, and as a result the [Int?] is Hashable as well!

let s: Set<[Int?]> = [[1, nil, 2], [3, 4], [5, nil, nil]]
s.contains([1,nil,2]) // returns true

Bool toggle

var isTheWeatherNice : Bool = true
print(isTheWeatherNice) // prints true
//now it's starts to rain
isTheWeatherNice.toggle() // it will change the bool value.
print(isTheWeatherNice) // prints false

Small, but in my opinion - very nice feature. I meet that extension for the first time while reading that objc.io blog posts.

Now it’s built into Swift 4.2. 🎉

Hashable protocol

protocol Hashable {
    func hash(into hasher: inout Hasher)

In Swift 4.2 we don’t have to provide custom algorithms for hashValue. Now swift handles a hash method quality with run performance. Important thing is that the hashValue use the random per-process seed which is created at the every app starts.

struct City: Hashable {
    let name : String
    let state : String
    let population : String
extension City : Hashable {
    func hash(into hasher: inout Hasher) {
        name.hash(into: &hasher)
        state.hash(into: &hasher)
let warsaw = City(name : "Warsaw", state: "Mazowieckie")
print(warsaw.hashValue) // will print hash value, using the Swift algorithms from hash function.

⚠️ In that approach, you should change the code that relates to the hashValue as a constant. In every application run, the hash value will be different. ⚠️

SE-0202 Random Unification

Swift 4.1 approach:

let randomIntFrom1to10 = 1 + (arc4random() % 10) // return random number is the 1...10

But in Swift 4.2 there is no need to use arc4random() anymore. 🎉

let randomIntFrom0To20 = Int.random(in: 0 ..< 20)
let randomFloat = Float.random(in: 0 ..< 1)

Super cool thing is that we can get a random value from Collection types like Array or Dictionary.

let names = ["John", "Paul", "Peter", "Tim"]

let playerNumberToName : [Int: String] = [9: "Lewandowski", 7: "Ronaldo"]

As you might notice, the randomElement function returns an Optional, because of the case where we call this function on the empty collection.

let emptyCollection : [String] = []
emptyCollection.randomElement() // retuns nil

Another new function are shuffle or shuffled functions.

let names = ["John", "Paul", "Peter", "Tim"]
let shuffledNames = names.shuffled() // returns an array of names in shuffled order.


It would be great to use those features in stable versions. My impressions from Xcode 10(beta) and Swift 4.2 was pretty amazing. I highly recommend you to watch What’s new in Swift talk from WWDC 2018

Below you can find a link to a GitHub gist with all features described above.



Kamil Wysocki

Kamil Wysocki

iOS developer, programmer

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