Swift constants file - class or structure?

Question

I want to create a Constants file in my Swift project - filled with static let string.

Should I create as a structure or class? And why?

Answer 1

With a class, you can create a subclass and, obviously, override class methods. If you use only static , there is no difference.

If the properties are value types, static if let someTypeProperty will be fine. If they are link types, additional help is required.

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Just some things with properties:

 struct PresetStringsStruct { static let someString : String = "Some Text" // struct static let someView : UIView = UIView(frame: CGRectZero) private init () { print("init") // never happens } } class PresetStringsClass { static let someString : String = "Some Text" // struct static let someView : UIView = UIView(frame: CGRectZero) private init () { print("init") // never happens } } 

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struct properties work as expected.

 // value properties var txtStruct = PresetStringsStruct.someString // "Some Text" txtStruct = "SomeOtherText" // "SomeOtherText" var txtStruct2 = PresetStringsStruct.someString // "Some Text" var txtClass = PresetStringsClass.someString // "Some Text" txtClass = "SomeOtherText" // "SomeOtherText" var txtClass2 = PresetStringsClass.someString // "Some Text" 

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When a property is a reference type , static properties return references to a single instance.

 // reference properties var viewStruct = PresetStringsStruct.someView viewStruct.frame = CGRect(x: 0, y: 0, width: 50, height: 50) var viewStruct2 = PresetStringsStruct.someView // CGRect(x: 0, y: 0, width: 50, height: 50) var viewClass = PresetStringsClass.someView viewClass.frame = CGRect(x: 0, y: 0, width: 50, height: 50) var viewClass2 = PresetStringsClass.someView // CGRect(x: 0, y: 0, width: 50, height: 50) 

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The only fool proof method I know of is by using static functions. . You can use class functions if you want to be able to subclass class and override functions. ( static does not allow overriding and is actually an alias for class final )

It also prevents the storage of too many type properties in memory . Unable to get rid of static let someProperty : Int = 0

 struct PresetStringsStruct { static func someStringFunc() -> String { return "SomeText" } static func someViewFunc() -> UIView { return UIView(frame: CGRectZero) } } class PresetStringsClass { static func someStringFunc() -> String { return "SomeText" } static func someViewFunc() -> UIView { return UIView(frame: CGRectZero) } } 

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Then it's up to you to make more sense. Since closing struct or class never used on their own, it does not matter. For me, a struct makes more sense, because I associate too much behavior with classes .

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You can also give more work and get rid of () , which results from using functions instead of properties.

 struct PresetStringsStruct { static var someString : String { get { return someStringFunc() } } static var someView : UIView { get { return someViewFunc() } } static func someStringFunc() -> String { return "SomeText" } static func someViewFunc() -> UIView { return UIView(frame: CGRectZero) } } var viewStruct = PresetStringsStruct.someView viewStruct.frame = CGRect(x: 0, y: 0, width: 50, height: 50) var viewStruct2 = PresetStringsStruct.someView // CGRect(x: 0, y: 0, width: 0, height: 0) 

Answer 2

You can use structs for static data - the best choice:

 struct staticStrings { static let name = "String1" static let age = "age1" } 

And to access data all over the world, just call staticStrings.name .

Why we use structs better than a class: Structures are preferable if they are relatively small and flexible, because copying is safer than plural reference to the same instance as classes.

Read More: Structures and Classes