Xcode6（Swift）で1つのプロジェクトから開発版とリリース版の2つのアプリを作りたい ref: http://qiita.com/matsuhisa@github/items/3f4e1ba0f05a69076dde

AppDelegate.swift

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?


    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        // Override point for customization after application launch.
        let splitViewController = self.window!.rootViewController as ViewController

        let size = CGSize(width: splitViewController.view.frame.size.width, height: 50)
        let postion:CGPoint  = CGPoint(x: 0, y: splitViewController.view.frame.size.height-50.0)
        let view:UIView      = UIView(frame: CGRect(origin: postion, size: size))


#if DEBUG
view.backgroundColor = UIColor(red: 255, green: 0.0, blue: 0.0, alpha: 0.5)
#else
view.backgroundColor = UIColor(red: 138, green: 138, blue:0, alpha: 1)
#endif


        let devInfoLabel   = UILabel()
        devInfoLabel.text  = "開発版：" + Constants().MESSEAGE

        devInfoLabel.font      = UIFont.systemFontOfSize(14)
        devInfoLabel.frame    = CGRect(origin: CGPoint(x: 10, y: splitViewController.view.frame.size.height-50.0), size: size)

        splitViewController.view.addSubview(view)
        splitViewController.view.addSubview(devInfoLabel)


        return true
    }

Constants.swift

import Foundation

class Constants:NSObject {
    #if DEBUG
    let MESSEAGE = "こんにちは（開発中です）"
    #else
    let MESSEAGE = "こんにちは"
    #endif
}

file2.txt

TARGETS > Build Settings > Swift Compiler - Custom Flags > Other Swift Flags

file3.txt

-D DEBUG

ViewController

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var LabelMessage: UILabel!
    override func viewDidLoad() {
        super.viewDidLoad()
        LabelMessage.text = Constants().MESSEAGE

        println(Constants().MESSEAGE)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}