Global constants file in Swift

Question

In my Objective-C projects I often use a global constants file to store things like notification names and keys for NSUserDefaults  It looks something like this    interface GlobalConstants   NSObject  extern NSString  someNotification    end   implementation GlobalConstants  NSString  someNotification     aaaaNotification     end   How do I do exactly the same thing in Swift

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Swift 4 Version  If you want to create a name for NotificationCenter   extension Notification Name       static let updateDataList1   Notification Name  updateDataList1       Subscribe to notifications   NotificationCenter default addObserver self  selector   selector youFunction   name   updateDataList1  object  nil    Send notification   NotificationCenter default post name   updateDataList1  object  nil    If you just want a class with variables to use   class Keys       static let key1    YOU KEY      static let key2    YOU KEY      Or   struct Keys       static let key1    YOU KEY      static let key2    YOU KEY

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Colors  extension UIColor       static var greenLaPalma  UIColor           return UIColor red 0 28  green 0 56  blue 0 22  alpha 1 00            Fonts  enum CustomFontType  String       case avenirNextRegular    AvenirNext-Regular       avenirDemiBold    AvenirNext-DemiBold     extension UIFont       static func getFont with type  CustomFontType  size  CGFloat  - gt  UIFont           let font   UIFont name  type rawValue  size  size            return font           For other - everything the same as in accepted answer

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Consider enumerations  These can be logically broken up for separate use cases   enum UserDefaultsKeys  String       case SomeNotification    aaaaNotification      case DeviceToken    deviceToken     enum PhotoMetaKeys  String       case Orientation    orientation hv      case Size    size      case DateTaken    date taken      One unique benefit happens when you have a situation of mutually exclusive options  such as   for  key  value  in photoConfigurationFile       guard let key   PhotoMetaKeys rawvalue  key  else           continue    invalid key  ignore it           switch  key        case Orientation            photo orientation   value           case Size            photo size   value                 In this example  you will receive a compile error because you have not handled the case of PhotoMetaKeys DateTaken

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Like others have mentioned  anything declared outside a class is global   You can also create singletons   class TestClass       static let sharedInstance   TestClass          Anything else goes here     var number   0     Whenever you want to use something from this class  you e g  write   TestClass sharedInstance number   1   If you now write println TestClass sharedInstance number  from anywhere in your project you will print 1 to the log  This works for all kinds of objects   tl dr  Any time you want to make everything in a class global  add static let sharedInstance   YourClassName   to the class  and address all values of the class with the prefix YourClassName sharedInstance

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Learn from Apple is the best way   For example  Apple s keyboard notification   extension UIResponder        public class let keyboardWillShowNotification  NSNotification Name      public class let keyboardDidShowNotification  NSNotification Name      public class let keyboardWillHideNotification  NSNotification Name      public class let keyboardDidHideNotification  NSNotification Name      Now I learn from Apple   extension User           user did login notification     static let userDidLogInNotification   Notification Name rawValue   User userDidLogInNotification         What s more  NSAttributedString Key foregroundColor   extension NSAttributedString        public struct Key   Hashable  Equatable  RawRepresentable            public init   rawValue  String           public init rawValue  String           extension NSAttributedString Key                                  Attributes                                 available iOS 6 0         public static let foregroundColor  NSAttributedString Key    UIColor  default blackColor      Now I learn form Apple   extension UIFont        struct Name              extension UIFont Name        static let SFProText Heavy    SFProText-Heavy      static let SFProText LightItalic    SFProText-LightItalic      static let SFProText HeavyItalic    SFProText-HeavyItalic       usage   let font   UIFont init name  UIFont Name SFProText Heavy  size  20      Learn from Apple is the way everyone can do and can promote your code quality easily

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According to the swift docs global variables are declared in file scope      Global variables are variables that are defined outside of any function  method  closure  or type context   Just create a swift file  E g  Constnats swift  and declare your constants there      Constants swift  let SOME NOTIF    aaaaNotification    and call it from anywhere in your project without the need to mention struct enum or class name      MyViewController swift  NotificationCenter default post name  SOME NOTIF  object  nil    I think this is much better for code readability

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For notifications you can use extension  something like this   extension Notification Name       static let testNotification    kTestNotification      And use it like NotificationCenter default post name   testNotification  object  nil

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To have global constants in my apps  this is what I do in a separate Swift file   import Foundation  struct Config       static let baseURL    https   api com       static APIKeys           static let token    token          static let user    user             struct Notifications           static let awareUser    aware user            It s easy to use  and to call everywhere like this   print Config Notifications awareUser

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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

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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

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Or just in GlobalConstants swift   import Foundation  let someNotification    aaaaNotification

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Constant swift import Foundation  let kBaseURL   NSURL string   quot http   www example com  quot    ViewController swift var manager   AFHTTPRequestOperationManager baseURL  kBaseURL

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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 swift struct 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 swift struct 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

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Caseless enums can also be be used    Advantage - They cannot be instantiated   enum API       enum Endpoint           static let url1    url1          static let url2    url2            enum BaseURL           static let dev    dev          static let prod    prod

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What I did in my Swift project 1  Create new Swift File 2  Create a struct and static constant in it  3  For Using just use YourStructName baseURL  Note  After Creating initialisation takes little time so it will show in other viewcontrollers after 2-5 seconds   import Foundation      struct YourStructName       static let MerchantID    XXX      static let MerchantUsername    XXXXX      static let ImageBaseURL    XXXXXXX      static let baseURL    XXXXXXX

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