Structs as namespace

IMO the best way to deal with that type of constants is to create a Struct.

struct Constants {    static let someNotification = "TEST"}

Then, for example, call it like this in your code:

print(Constants.someNotification)

Nesting

If you want a better organization I advise you to use segmented sub structs

struct K {    struct NotificationKey {        static let Welcome = "kWelcomeNotif"    }    struct Path {        static let Documents = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0] as String        static let Tmp = NSTemporaryDirectory()    }}

Then you can just use for instance K.Path.Tmp

Real world example

This is just a technical solution, the actual implementation in my code looks more like:

struct GraphicColors {    static let grayDark = UIColor(0.2)    static let grayUltraDark = UIColor(0.1)    static let brown  = UIColor(rgb: 126, 99, 89)    // etc.}

and

enum Env: String {    case debug    case testFlight    case appStore}struct App {    struct Folders {        static let documents: NSString = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0] as NSString        static let temporary: NSString = NSTemporaryDirectory() as NSString    }    static let version: String = Bundle.main.object(forInfoDictionaryKey: "CFBundleShortVersionString") as! String    static let build: String = Bundle.main.object(forInfoDictionaryKey: "CFBundleVersion") as! String    // This is private because the use of 'appConfiguration' is preferred.    private static let isTestFlight = Bundle.main.appStoreReceiptURL?.lastPathComponent == "sandboxReceipt"    // This can be used to add debug statements.    static var isDebug: Bool {        #if DEBUG        return true        #else        return false        #endif    }    static var env: Env {        if isDebug {            return .debug        } else if isTestFlight {            return .testFlight        } else {            return .appStore        }    }}

I am abit late to the party.

No matter here's how i manage the constants file so that it makes more sense to developers while writing code in swift.

FOR URL:

//URLConstants.swift  struct APPURL {    private struct Domains {        static let Dev = "http://test-dev.cloudapp.net"        static let UAT = "http://test-UAT.com"        static let Local = "192.145.1.1"        static let QA = "testAddress.qa.com"    }    private  struct Routes {        static let Api = "/api/mobile"    }    private  static let Domain = Domains.Dev    private  static let Route = Routes.Api    private  static let BaseURL = Domain + Route    static var FacebookLogin: String {        return BaseURL  + "/auth/facebook"    }}

For CUSTOMFONTS:

//FontsConstants.swiftstruct FontNames {    static let LatoName = "Lato"    struct Lato {        static let LatoBold = "Lato-Bold"        static let LatoMedium = "Lato-Medium"        static let LatoRegular = "Lato-Regular"        static let LatoExtraBold = "Lato-ExtraBold"    }}

FOR ALL THE KEYS USED IN APP

//KeyConstants.swift    struct Key {        static let DeviceType = "iOS"        struct Beacon{            static let ONEXUUID = "xxxx-xxxx-xxxx-xxxx"        }        struct UserDefaults {            static let k_App_Running_FirstTime = "userRunningAppFirstTime"        }        struct Headers {            static let Authorization = "Authorization"            static let ContentType = "Content-Type"        }        struct Google{            static let placesKey = "some key here"//for photos            static let serverKey = "some key here"        }        struct ErrorMessage{            static let listNotFound = "ERROR_LIST_NOT_FOUND"            static let validationError = "ERROR_VALIDATION"        }    }

FOR COLOR CONSTANTS:

//ColorConstants.swiftstruct AppColor {    private struct Alphas {        static let Opaque = CGFloat(1)        static let SemiOpaque = CGFloat(0.8)        static let SemiTransparent = CGFloat(0.5)        static let Transparent = CGFloat(0.3)    }    static let appPrimaryColor =  UIColor.white.withAlphaComponent(Alphas.SemiOpaque)    static let appSecondaryColor =  UIColor.blue.withAlphaComponent(Alphas.Opaque)    struct TextColors {        static let Error = AppColor.appSecondaryColor        static let Success = UIColor(red: 0.1303, green: 0.9915, blue: 0.0233, alpha: Alphas.Opaque)     }    struct TabBarColors{        static let Selected = UIColor.white        static let NotSelected = UIColor.black    }    struct OverlayColor {        static let SemiTransparentBlack = UIColor.black.withAlphaComponent(Alphas.Transparent)        static let SemiOpaque = UIColor.black.withAlphaComponent(Alphas.SemiOpaque)        static let demoOverlay = UIColor.black.withAlphaComponent(0.6)    }}

You can wrap these all files in a common group named Constants in your Xcode Project.

And for more watch this video

Although I prefer @Francescu's way (using a struct with static properties), you can also define global constants and variables:

let someNotification = "TEST"

Note however that differently from local variables/constants and class/struct properties, globals are implicitly lazy, which means they are initialized when they are accessed for the first time.

Suggested reading: Global and Local Variables, and also Global variables in Swift are not variables