SongPoll3.swift

import Foundation

struct Song {
	var title: String
	var length: Float

	mutating func addAdvertisement() {
		self.title += " plus commercial"
		self.length += 10
	}
}

var song = Song(title: "Aerials", length: 240)
song.addAdvertisement()
print(song.length)

or even more functional: https://gist.github.com/fabb/2b0d390e077b130927cc