Protocol extensions and typed arrays

Swift 2.0 introduces protocol extensions, aswel as typed array extensions. This makes it possible to extend an array containing a specific type or even add methods to class inheriting a specific protocol.

Typed array protocol extensions

With typed array extensions you can create methods for Arrays containing a specific type only. For example, if you have a Person struct which inherits the TextRepresentable protocol:

struct Person {
    var name: String
    var age: Int

protocol TextRepresentable {
    func asText() -> String

// Person inherits TextRepresentable protocol
extension Person: TextRepresentable {
    func asText() -> String {
        return "Person named \(name) aged \(age)"

You can create an extension to Array’s containing objects which inherit from TextRepresentable:

extension CollectionType where Generator.Element : TextRepresentable {
    func commaSeperatedString() -> String {
        return ", ".join(map({$0.asText()}))

Which allows you to call it like this:

let personOne = Person(name: "Jan", age: 30)
let personTwo = Person(name: "Ellis", age: 28)
let persons:[Person] = [personOne, personTwo]

let string = persons.commaSeperatedString()
// Prints out "Person named Jan aged 30, Person named Ellis aged 28"

Antoine van der Lee

Dutch iOS developer at Triple. Developed apps like Buienradar, Videoland and Pop the Dots.

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