Swift version: 5.6
Generics are a way of making one data type act in a variety of ways depending on how it is created. You’ve already used them whether you realized or not: Swift has an Array
type, but it is generic – it doesn’t contain any sort of specific data. Instead, you ask for arrays that hold specific kinds of data by using things like [String]
to get a string array.
It’s not hard to create generics of your own, and to demonstrate that we’re going to create a simple Queue
type. These are first-in, first-out data structures (FIFO), which means you add things to the back and remove them from the front – much like a real-life queue.
We want this queue to be generic, and in Swift you do that by writing the name of a generic placeholder inside angle brackets, like this: struct Queue<T> {
. That T
doesn’t mean anything special – it could have been R
or Element
– but T
is commonly used.
Inside the queue we’re going to have an internal array tracking the items we’re storing, and we’ll write methods to add and remove items.
Here’s the complete Queue
struct:
struct Queue<T> {
private var internalArray = [T]()
var count: Int {
return internalArray.count
}
mutating func add(_ item: T) {
internalArray.append(item)
}
mutating func remove() -> T? {
if internalArray.count > 0 {
return internalArray.removeFirst()
} else {
return nil
}
}
}
You can now create a queue to store any object you want. For example, this create a queue of integers:
let queue = Queue<Int>()
SAVE 50% To celebrate WWDC23, all our books and bundles are half price, so you can take your Swift knowledge further without spending big! Get the Swift Power Pack to build your iOS career faster, get the Swift Platform Pack to builds apps for macOS, watchOS, and beyond, or get the Swift Plus Pack to learn advanced design patterns, testing skills, and more.
Available from iOS 8.0 – learn more in my book Pro Swift
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.
Link copied to your pasteboard.