我感觉它和java或go里的接口，差不多一个意思吧。

protocol FullyNamed {
	var fullName: String { get }
}

struct Person: FullyNamed {
	var fullName: String
}

class Starship: FullyNamed {
	var prefix: String?
	var name: String
	init(name: String, prefix: String? = nil) {
		self.name = name
		self.prefix = prefix
	}
	var fullName: String {
		return (prefix != nil ? prefix! + " " : "") + name
	}
}

var ncc1701 = Starship(name: "Enterprise", prefix: "USS")
print(ncc1701.fullName)


let john = Person(fullName: "John Appleseed")
print(john.fullName)

protocol RandomNumberGenerator {
	func random() -> Double
}

class LinearCongruentialGenerator: RandomNumberGenerator {
	var lastRandom = 42.0
	let m = 139968.0
	let a = 3877.0
	let c = 29573.0
	func random() -> Double {
		lastRandom = (lastRandom * a + c)
		return lastRandom / m
		
	}
}

let generator = LinearCongruentialGenerator()
print("Here's random number: \(generator.random())")
print("And another one: \(generator.random())")

protocol Togglable {
	mutating func toggle()
}

enum OnOffSwitch: Togglable {
	case Off, On
	mutating func toggle() {
		switch self {
			case Off:
				self = On
			case On:
				self = Off
		}
	}
}

var lightSwitch = OnOffSwitch.Off
lightSwitch.toggle()
print(lightSwitch)