swiftstaticconstants

What is the use of "static" keyword if "let" keyword used to define constants/immutables in swift?


I'm little bit confused about using static keyword in swift. As we know swift introduces let keyword to declare immutable objects. Like declaring the id of a table view cell which most likely won't change during its lifetime. Now what is the use of static keyword in some declaration of struct like:

struct classConstants
{
    static let test = "test"
    static var totalCount = 0
}

whereas let keyword do the same.In Objective C we used static to declare some constant like

static NSString *cellIdentifier=@"cellId";

Besides which makes me more curious is the use of static keyword along with let and also var keyword. Can anybody explain me where to use this static keyword? More importantly do we really need static in swift?


Solution

  • I will break them down for you:

    • var : used to create a variable
    • let : used to create a constant
    • static : used to create type properties with either let or var. These are shared between all objects of a class.

    Now you can combine to get the desired out come:

    • static let key = "API_KEY" : type property that is constant
    • static var cnt = 0 : type property that is a variable
    • let id = 0 : constant (can be assigned only once, but can be assigned at run time)
    • var price = 0 : variable

    So to sum everything up var and let define mutability while static and lack of define scope. You might use static var to keep track of how many instances you have created, while you might want to use just varfor a price that is different from object to object. Hope this clears things up a bit.

    Example Code:

    class MyClass{
        static let typeProperty = "API_KEY"
        static var instancesOfMyClass = 0
        var price = 9.99
        let id = 5
    
    }
    
    let obj = MyClass()
    obj.price // 9.99
    obj.id // 5
    
    MyClass.typeProperty // "API_KEY"
    MyClass.instancesOfMyClass // 0