Hands-On Design Patterns with Swift

Adding requirements to protocols 

Empty protocols can be useful as we've seen previously, but protocols are meant to provide requirements.

Protocols can require different aspects of objects:

• Properties, their type, and accessibility
• Methods
• Initializers

protocol DemoProtocol {    var aRequiredProperty: String { get set }    var aReadonlyProperty: Double { get }    static var aStaticProperty: Int { get set }    init(requiredProperty: String)    func doSomething() -> Bool }

The previous DemoProtocol protocol exposes all of the requirements a conforming class should provide:

• aRequiredProperty should be String that can be read and written. 
• aReadonlyProperty should be Double, but should only be at least readable. Conforming classes can implement it as