Storyboard segue navigation in Swift 2

MasterViewController.swift

import UIKit

final class MasterViewController: UIViewController {
    @IBAction func showDetails(sender: UIButton) {
        performSegueWithIdentifier("ShowDetails", sender: sender)
    }

    override func prepareForSegue(
        segue: UIStoryboardSegue,
        sender: AnyObject?
    ) {
        if segue.identifier == "ShowDetails" {
            let details = segue.destinationViewController
                as! DetailViewController
            details.message = "Hello from the first screen"
        }
    }
}

final class DetailViewController: UIViewController {
    @IBOutlet weak var messageLabel: UILabel!
    var message: String!

    override func viewDidLoad() {
        super.viewDidLoad()
        messageLabel.text = message
    }
}