Join string array with separator “, ” and add “, and ” to join the last element in Swift

Question

I\'m messing around with parsing JSON with SwiftyJSON on a swift playground. My code is as follows:

import UIKit
import SwiftyJSON

var partyList: [String] =         


        

Answer 1

Since iOS 13.0+ / macOS 10.15+ Apple provides the ListFormatter. See also here for details.

Arrays can be formatted as easy as:

let elements = ["a", "b", "c"]
result = ListFormatter.localizedString(byJoining: elements)

As the function name suggests, you also get the localization for free.

Answer 2

Add a condition to check if your String collection has less than or is equal to 2 elements, if true just return the two elements joined by " and " otherwise drop the last element of your collection, join the elements with a separator ", " then re add the last element with the final separator ", and ".

You can extend BidirectionalCollection protocol constraining its elements to the StringProtocol:

Bidirectional collections offer traversal backward from any valid index, not including a collection’s startIndex. Bidirectional collections can therefore offer additional operations, such as a last property that provides efficient access to the last element and a reversed() method that presents the elements in reverse order.

Xcode 11.4 • Swift 5.2 or later

extension BidirectionalCollection where Element: StringProtocol {
    var sentence: String {
        count <= 2 ?
            joined(separator: " and ") :
            dropLast().joined(separator: ", ") + ", and " + last!
    }
}

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let elements = ["a", "b", "c"]
let sentenceFromElements = elements.sentence   // "a, b, and c"