extension_computed_property.swift

protocol ActivityIndicatorProtocol: class {
    var activityIndicator: UIView? { get set }
}

extension ActivityIndicatorProtocol {
    
    var activityIndicator: UIView? {
        get {
            // getter code
            return nil
        }
        set {
            // setter code
            print("\(newValue)")
        }
    }
    
}