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I begin my project with a split view controller as initial view controller and start it automatically from storyboard.

Generally, an app with this UI have one and only one split view controller as root, so I create a static variable in the subclass and set it when initialisation was done.

So I want try this behaviour with swift.

I read the Swift programming language guide book on iBook about Type properties (with static and class keyword) and trying a piece of code to the job: 

import UIKit class SplitViewController: UISplitViewController { class func sharedInstance() -> SplitViewController { return SplitViewController.instance } class let instance: SplitViewController = nil init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: NSBundle?) { super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil) self.initialization() } init(coder aDecoder: NSCoder!) { super.init(coder: aDecoder); self.initialization() } func initialization() { SplitViewController.instance = self; } }

but I figured out when Xcode say the class keyword for type properties wasn't supported yet.

error detail in image

Did you have a solution to do this ?

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14
  • What happens if you replace 'let' with 'var'? Commented Jun 3, 2014 at 12:46
  • It yields the same error. Commented Jun 3, 2014 at 12:47
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    It's the first seed, calm down. :) If the book says it's supported and it's not yet available, it will be. Even the error says "yet". Commented Jun 3, 2014 at 12:48
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    Yes @akashivskyy you've reason but may be it could be and error on my side and someone have a solution to do this behavior... Commented Jun 3, 2014 at 12:51
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    @lespommes Apple is notoriously tight-lipped about anything that's pending. It's embarrassing for them that such a standard and obvious feature was lacking from their huge release of their new flagship language. There are many improvements required before Swift is ready for serious use. Commented Feb 3, 2015 at 18:28

12 Answers 12

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71

Embedding a struct can work just fine as a workaround:

class SomeClass { // class var classVariable: Int = 0 // "Class variables not yet supported." Weird. // Workaround: private struct SubStruct { static var staticVariable: Int = 0 } class var workaroundClassVariable: Int { get { return SubStruct.staticVariable } set { SubStruct.staticVariable = newValue } } }

The SomeClass.workaroundClassVariable computed type property can then be used as if it were a stored type property.

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2 Comments

Worked for me - except as I had to drop the 'public' as XCode 6.0 did not like me declaring a public class within an internal class.
Works great, except that xcode does not allow nested type in a generic type... so if you have a generic class, it seems rather hopeless as only computed properties are possible.
37

Swift now has support for static variables in classes. This is not exactly the same as a class variable (because they aren't inherited by subclasses), but it gets you pretty close:

class X { static let y: Int = 4 static var x: Int = 4 } println(X.x) println(X.y) X.x = 5 println(X.x)
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7 Comments

As Bill says, that's the not the same but that's I need !
@VincentSaluzzo, (and Bill) What the difference between this and class variable?
The Apple documentation have changed recently to update status : developer.apple.com/library/ios/documentation/Swift/Conceptual/… In fact, class keyword can only used for computed properties now and static are for all type properties (in enum, class or struct)
@skywinder As I mentioned in my answer, true class variables can be inherited by subclasses. Static variables can't.
@VincentSaluzzo Does Apple update its document? developer.apple.com/library/ios/documentation/Swift/Conceptual/… look at the fourth paragraph: "For value types (that is, structures and enumerations), you can define stored and computed type properties. For classes, you can define computed type properties only."
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19

It seems to be possible to declare variables with static storage duration in file scope (as in C):

var sharedInstance: SplitViewController? = nil class SplitViewController: UISplitViewController { .... func initialization() { sharedInstance = self } }
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5 Comments

mmmh, why not, but define a var at file scope doesn't do a memory leak in a long time usage ?
@VincentSaluzzo There's no difference to what you did before Swift: store the sole instance in a static variable. There's nothing to be leaked here, except the single instance which lives as long as the process.
I tried this in playground with my own class. It doesn't work 'cos the class has not be declared yet when you initialized that "static" var. I have not tried it in Xcode project (i guess it must have worked there?). So I may need to figure out "class forward declaration" like you always do when specifying protocol for a class.
Note that in Xcode 6.0, you cannot have two file scope variables with the same name, even if they are private.
@NikolayTsenkov Exactly.
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My preferred method is to just use a private file scope var outside of the class and then implement class/static getters and setters:

private var _classVar: Int = 0; class SomeClass { public class var classVar: Int { get { return _classVar } set { _classVar = newValue } } }
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5

As of Swift 1.2 (available with Xcode 6.3b1 and onwards), static class properties and methods are supported.

class SomeClass { static var someVariable: Int = 0 }
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2 Comments

Did you catch if they just deprecated the class variable, or is there a distinction (used to be static for structs, class for classes)?
@chrisco The release notes state that static is an alias for class final.
4

Using a dispatch_once singleton model in Swift

Seems to be the best answer so far, avoiding the use of a global variable.

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4

A solution enough similar than var in file scope but more customisable and near singleton is to use a struct which support static var as property of class

struct PersonSharedData { static var backstore = "" var data: String { get { return PersonSharedData.backstore } set { PersonSharedData.backstore = newValue } } } class Person { var shared=PersonSharedData() //<< pseudo class var var family: String { get { return shared.data } set { shared.data=newValue } } var firstname = "" var lastname = "" var sexe: Sexe = .Unknown }
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2

Ok, with the solution of Nikolai that do the work. I post my changes in this thread for information

var instance: SplitViewController? = nil class SplitViewController: UISplitViewController { class func sharedInstance() -> SplitViewController? { return instance; } init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: NSBundle?) { super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil) self.initialization() } init(coder aDecoder: NSCoder!) { super.init(coder: aDecoder); self.initialization() } func initialization() { instance = self } }

and for example, in my appDelegate, I can access this static method like this 

SplitViewController.sharedInstance()!.presentsWithGesture = false
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1 Comment

I'm just curious, but isn't the variable "instance" a global variable then? This would mean that if you have another singleton class your variable "instance" would be overwritten, right?
1

The wording in the error heavily implies this will be a language feature in the future.

You may want to resort temporarily to declaring a property variable in the Application Delegate and retrieve it from there. Not ideal, definitely an anti-pattern, but would give you a central place to retrieve the UISplitViewController when needed.

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1 Comment

No because in my case, the SplitViewController was initizalize by runtime when awake from storyboard, so I can't directly access to this view controller from my application delegate
1

You have to wrap the class variables inside an inner struct variable

class Store{ var name:String var address:String var lat:Int var long:Int init(name:String, address:String, lat:Int, long:Int){ self.name = name self.address = address self.lat = lat self.long=long } private struct FACTORY_INITIALIZED_FLAG { static var initialized: Bool = false static var myStoreList:[Store]? static func getMyStoreList()->[Store]{ if !initialized{ println("INITIALIZING") myStoreList = [ Store(name: "Walmart", address: "abcd", lat: 10, long: 20), Store(name: "JCPenny", address: "kjfnv", lat: 23, long: 34) ] initialized = true } return myStoreList! } } } var a = Store.FACTORY_INITIALIZED_FLAG.getMyStoreList() var b = Store.FACTORY_INITIALIZED_FLAG.getMyStoreList() // only prints INITIALIZING once
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0

Try this:

class var instance: SplitViewController { return nil }
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0

It is called Type Property in Swift.

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. The example below shows the syntax for stored and computed type properties:

struct SomeStructure { static var storedTypeProperty = "Some value." static var computedTypeProperty: Int { return 1 } } enum SomeEnumeration { static var storedTypeProperty = "Some value." static var computedTypeProperty: Int { return 6 } } class SomeClass { static var storedTypeProperty = "Some value." static var computedTypeProperty: Int { return 27 } class var overrideableComputedTypeProperty: Int { return 107 } }

Read more at link below,

https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Properties.html#//apple_ref/doc/uid/TP40014097-CH14-ID254

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