Static vs class functions variables in Swift classes

Question

The following code compiles in Swift 1 2   class myClass       static func myMethod1               class func myMethod2               static var myVar1         func doSomething         myClass myMethod1       myClass myMethod2       myClass myVar1    abc      What is the difference between a static function and a class function  Which one should I use  and when   If I try to define another variable class var myVar2       it says      Class stored properties not yet supported in classes  did you mean  static     When this feature is supported  what will the difference be between a static variable and a class variable  i e  when both are defined in a class   Which one should I use  and when    Xcode 6 3

User · Answer

There s one more difference  class can be used to define type properties of computed type only  If you need a stored type property use static instead    You define type properties with the static keyword  For computed type properties for class types  you can use the class keyword instead to allow subclasses to override the superclass   s implementation

User · Answer

static and class both associate a method with a class  rather than an instance of a class  The difference is that subclasses can override class methods  they cannot override static methods   class properties will theoretically function in the same way  subclasses can override them   but they re not possible in Swift yet

User · Answer

I got this confusion in one of my project as well and found this post  very helpful  Tried the same in my playground and here is the summary  Hope this helps someone with stored properties and functions of type static  final class  overriding class vars etc   class Simple        init    print  init method called in base         class func one    print  class - one           class func two    print  class - two           static func staticOne    print  staticOne           static func staticTwo    print  staticTwo           final func yesFinal    print  yesFinal           static var myStaticVar    static var in base         Class stored properties not yet supported in classes  did you mean  static       class var myClassVar1    class var1         This works fine     class var myClassVar  String          return  class var in base           class SubSimple  Simple         Successful override     override class func one             print  subClass - one                 Successful override     override class func two              print  subClass - two                  Error  Class method overrides a  final  class method     override static func staticOne                   error  Instance method overrides a  final  instance method     override final func yesFinal                   Works fine     override class var myClassVar  String           return  class var in subclass            And here is the testing samples   print Simple one    print Simple two    print Simple staticOne    print Simple staticTwo    print Simple yesFinal Simple     print SubSimple one    print Simple myStaticVar  print Simple myClassVar  print SubSimple myClassVar     Output class - one   class - two   staticOne   staticTwo   init method called in base  Function  subClass - one   static var in base class var in base class var in subclass

User · Answer

Testing in Swift 4 shows performance difference in simulator  I made a class with  class func  and struct with  static func  and ran them in test    static func is    20  faster without compiler optimization 38  faster when optimization -whole-module-optimization is enabled     However  running the same code on iPhone 7 under iOS 10 3 shows exactly the same performance    Here is sample project in Swift 4 for Xcode 9 if you like to test yourself  https   github com protyagov StructVsClassPerformance

User · Answer

I tried mipadi s answer and comments on playground  And thought of sharing it  Here you go  I think mipadi s answer should be mark as accepted   class A      class func classFunction              static func staticFunction              class func classFunctionToBeMakeFinalInImmediateSubclass             class B  A       override class func classFunction                  Compile Error  Class method overrides a  final  class method     override static func staticFunction                  Lets avoid the function called  classFunctionToBeMakeFinalInImmediateSubclass  being overriden by subclasses         First way of doing it     override static func classFunctionToBeMakeFinalInImmediateSubclass                         Second way of doing the same     override final class func classFunctionToBeMakeFinalInImmediateSubclass                 To use static or final class is choice of style        As mipadi suggests I would use  static at super class  and final class to cut off further overrides by a subclass    class C  B        Compile Error  Class method overrides a  final  class method     override static func classFunctionToBeMakeFinalInImmediateSubclass

User · Answer

Regarding to OOP  the answer is too simple   The subclasses can override class methods  but cannot override static methods   In addition to your post  if you want to declare a class variable  like you did class var myVar2        you should do it as follow   class var myVar2  String       return  whatever you want

User · Answer

class vs static class is used inside Reference Type class    computed property method can be overridden by subclass  static is used inside Reference Type and Value Type class  enum    computed property and stored property method cannot be changed by subclass  protocol MyProtocol         class var protocolClassVariable   Int   get    ERROR  Class properties are only allowed within classes     static var protocolStaticVariable   Int   get              class func protocolClassFunc    ERROR  Class methods are only allowed within classes     static func protocolStaticFunc      struct ValueTypeStruct  MyProtocol         MyProtocol implementation begin     static var protocolStaticVariable  Int   1          static func protocolStaticFunc                          MyProtocol implementation end            class var classVariable    quot classVariable quot   ERROR  Class properties are only allowed within classes     static var staticVariable    quot staticVariable quot         class func classFunc        ERROR  Class methods are only allowed within classes     static func staticFunc         class ReferenceTypeClass  MyProtocol         MyProtocol implementation begin     static var protocolStaticVariable  Int   2          static func protocolStaticFunc                          MyProtocol implementation end          var variable    quot variable quot         class var classStoredPropertyVariable    quot classVariable quot   ERROR  Class stored properties not supported in classes      class var classComputedPropertyVariable  Int           get               return 1                      static var staticStoredPropertyVariable    quot staticVariable quot       static var staticComputedPropertyVariable  Int           get               return 1                      class func classFunc          static func staticFunc         final class FinalSubReferenceTypeClass  ReferenceTypeClass       override class var classComputedPropertyVariable  Int           get               return 2                     override class func classFunc           class SubFinalSubReferenceTypeClass  FinalSubReferenceTypeClass      ERROR  Inheritance from a final class    Reference vs Value Type

User · Answer

Adding to above answers static methods are static dispatch means the compiler know which method will be executed at runtime as the static method can not be overridden while the class method can be a dynamic dispatch as subclass can override these

User · Answer

There s one more difference  class can be used to define type properties of computed type only  If you need a stored type property use static instead   Class  - reference type  struct  - value type

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