What are static methods and variables?

Swift version: 5.6

Paul Hudson @twostraws May 28th 2019

Static methods and variables belong to the type that defined them, rather than instances of that type. For example, we could create a struct to track taxis in a city, like this:

struct Taxi1 {
    var ownerName: String
    var licensePlate: String
}

Each instance of that struct will have its own ownerName and licensePlate property strings. However, if we made a static property inside that struct then it would be shared by all taxis. For example, we could add this property to store how many taxis exist in the city:

struct Taxi2 {
    var ownerName: String
    var licensePlate: String
    static var count: Int = 0
}

When we want to reference that property we need to use Taxi2.count, because it belongs to the struct not to instances of that struct.

The same is true of static methods, which are sometimes called “type methods” – they belong to the struct or class that defined them rather than instance of the class. In practice that means you can’t use self inside the method because there is no instance to refer to.