Join an array of strings with a different final delimiter

Question

Generally: How do I join an array of stings such that the last delimiter is different than the others?

Specifically: How does the iOS Messages app construct the default name of a group conversation, which is a list of contacts' names?

Example

class User {
    var name: String

    init(name: String) {
        self.name = name
    }
}

let users = [
    User(name: "Matthew"),
    User(name: "Mark"),
    User(name: "Luke"),
    User(name: "John")
]

users.list(" & ") { $0.name } // => "Matthew, Mark, Luke & John"

PHP

• Implode array with ", " and add "and " before last item
• Replace the last comma with an & sign
• How to edit the implode so it will join values with two strings?

Ruby (on Rails)

• Rails join a list of strings with commas and "and" before the last

Python

• How to join list in Python but make the last separator different?

C# (Linq)

• Comma separated list with "and" in place of the last comma

Answer 1

Using the class defined in the question you could do something like this:

let names = users.map { $0.name }
let suffix = names.suffix(2)
let joined = (names.dropLast(suffix.count) + [suffix.joinWithSeparator(" & ")]).joinWithSeparator(", ")

print(joined)   // prints Matthew, Mark, Luke & John