Oftentimes, we find ourselves being more concerned with data being changed and not so concerned about who can read it. When this is the case, it is possible to implement a private setter. A private setter allows us to limit write access to within the scope of the struct but still allow the property to be read outside of the struct.

We use the (set) keyword when we want to declare a private setter:

struct Cat {
    private(set) var numberOfLives : Int
}

In this example, we declare the setter to have private level access, while the getter will be the default internal level access. Note that we could have also declared the numberOfLives variable like so:

struct Cat {
    public private(set) var numberOfLives : Int = 9
}

var scrambles = Cat()

// Prints: 9
print(scrambles.numberOfLives)

// This causes a compiler error due to invalid access
scrambles.numberOfLives = 10

This gives the getter for numberOfLives public level access, while the setter has private level access. Any combination of access levels can be declared, as long as the setter has a lower access level than the getter. For example open fileprivate(set) is a valid access level, while private internal(set) would be an invalid access level.