This article is to highlight the key features added/ modified in Swift 4. Apple scheduled to release Swift 4 in fall 2017 and its beta versions are already available for download for developers.

Downloading Swift 4 Snapshot

Swift 4.0 Snapshots are prebuilt binaries that are automatically created from swift-4.0-branch branch. Latest snapshot package downloaded from Swift 4.0 Development section from here.

Run downloaded installer file to install the snapshot. Now goto Xcode->Toolchains and select the snapshot as in below screenshot.

There is nothing more to do; you are all set to play with Swift 4. Create new playground file and test it out yourself all the new Swift 4 features.

Here, I covered the important new/modified features and I will keep adding here as I get more details

Strings

String is a collection

Strings are now collections in Swift 4 like it was in Swift 2. This allows iterating though characters in string. Just like any other collection, string can reversed, apply map() and flatmap() !

let swift4String = "String is collection of characters in Swift4"
for char in swift4String.reversed() {
    print(char) // prints each character in reversed string
}

Multi-line string literals

Swift 3 requires line break (\n) to write multi-line strings. In Swift 4 introduces triple quotes (“””) to start and end of the multiline string. It lets use quote marks without escaping.

The indentation of the closing delimiter determines how much whitespace is stripped from the start of each line.

var multiStr =
"""
This string starts with a line feed.
It also ends with a line feed.
"""

print(multiStr)

This image demonstrates on how indentation works

Substring is new type

Swift 4 introduced Substring type to represent the String slices.

var str = "Hello, playground"
let commaIndex = str.index(of: ",")!
let substring = str.substring(to: commaIndex)  // Hello
print(type(of: substring))    //String

let substringRange = str[..<commaIndex]
print(type(of: substringRange))  //Substring

The need for introducing Substring is to optimize memory for Strings. I will create a separate article on memory management and talk about Substring there.

Unicode 9 Characters

Each String emoticon is now 1 character in Swift 4.

"👩‍👩‍👧".count  //is 1 in Swift 4
"👩‍👩‍👧".characters.count   //is 3 in swift 3