Swift - Using extensions to define default implementations of your protocols

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Introduction

A default implementation lets you write a sensible implementation of parts of the protocol that will be used when classes conforming to the protocol don't provide them: 


protocol Runnable { 
    // This property must be at least gettable 
    var isRuning  : Bool { get } 

    // This property must be gettable and settable 
    var runningSpeed: Double { get set } 

    // This function must exist, but what it does is up to the implementor 
    func startRuning(runningSpeed: Double) -> Void 
} 
extension Runnable 
{ 
    func startRuning(runningSpeed: Double) { 
        print("I am running") 
    } 
}

With this default implementation of Runnable, if we now create a new class and don't provide the method call, it will still work: 

class AnotherBlinker  : Blinkable { 
    var isBlinking: Bool = true 

    var blinkSpeed: Double = 0.0 
} 
let anotherBlinker = AnotherBlinker() 
anotherBlinker.startBlinking(blinkSpeed: 3)

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