Access control

Access control lets you restrict which code can use properties and methods. This is important because you might want to stop people reading a property directly, for example.

We could create a Person struct that has an id property to store their social security number:

struct Person {
    var id: String

    init(id: String) {
        self.id = id
    }
}

let ed = Person(id: "12345")

Once that person has been created, we can make their id be private so you can’t read it from outside the struct – trying to write ed.id simply won’t work.

Just use the private keyword, like this:

struct Person {
    private var id: String

    init(id: String) {
        self.id = id
    }
}

Now only methods inside Person can read the id property. For example:

struct Person {
    private var id: String

    init(id: String) {
        self.id = id
    }

    func identify() -> String {
        return "My social security number is \(id)"
    }
}

Another common option is public, which lets all other code use the property or method.