NEW: Master Swift design patterns with my latest book! >>

< Previous: Constants   Next: Simple types: Summary >

Type annotations

Swift assigns each variable and constant a type based on what value it’s given when it’s created. So, when you write code like this Swift can see it holds a string:

let str = "Hello, playground"

That will make str a string, so you can’t try to assign it an integer or a boolean later on. This is called type inference: Swift is able to infer the type of something based on how you created it.

If you want you can be explicit about the type of your data rather than relying on Swift’s type inference, like this:

let album: String = "Reputation"
let year: Int = 1989
let height: Double = 1.78
let taylorRocks: Bool = true

Notice that booleans have the short type name Bool, in the same way that integers have the short type name Int.

Love Hacking with Swift?

Get all 40 projects in PDF and HTML: buy the Hacking with Swift book! It contains over 1300 pages of hands-on Swift coding, and will really help boost your iOS career

< Previous: Constants   Next: Simple types: Summary >
Click here to visit the Hacking with Swift store >>