进入机械的学习模式，

就是把代友敲完。

以期能加深些记忆。

struct Resolution {
	var width = 0
	var height = 0
}

class VideoMode {
	var resolution = Resolution()
	var interlaced = false
	var frameRate = 0.0
	var name: String?
}

let someResolution = Resolution(width: 640, height: 480)
let someVideoMode = VideoMode()

print("The width of someResolution is \(someResolution.width)")

someVideoMode.resolution.width = 1280
print("The width of someVedioMode is \(someVideoMode.resolution.width)")

let hd = Resolution(width: 1920, height: 1080)
var cinema = hd
cinema.width = 2048

print("cienma is now \(cinema.width) pixels wide")
print("hd is still \(hd.width) pixels width")

enum CompassPoint {
	case North, South, East, West
}

var currentDirection = CompassPoint.West
let rememberedDirection = currentDirection
currentDirection = .East
if rememberedDirection == .West {
	print("The remembered direction is still .West")
}

let tenEighty = VideoMode()
tenEighty.resolution = hd
tenEighty.interlaced = true
tenEighty.name = "1080i"
tenEighty.frameRate = 25.0

let alsoTenEighty = tenEighty
alsoTenEighty.frameRate = 30.0

print("The frameRate property of tenEighty is now \(tenEighty.frameRate)")

struct Point {
	var x = 0.0, y = 0.0
}

struct Size {
	var width = 0.0, height = 0.0
}

struct Rect {
	var origin = Point()
	var size = Size()
	var center: Point {
		get {
			let centerX = origin.x + (size.width / 2)
			let centerY = origin.y + (size.height / 2)
			return Point(x: centerX, y: centerY)
		}
		set(newCenter) {
			origin.x = newCenter.x - (size.width / 2)
			origin.y = newCenter.y - (size.height / 2)
		}
	}
}

var square = Rect(origin: Point(x: 0.0, y: 0.0),
	size: Size(width: 10.0, height: 10.0))
	
let initialSquareCenter = square.center
square.center = Point(x: 15.0, y: 15.0)
print("square.origin is now at (\(square.origin.x), \(square.origin.y))")

class StepCounter {
	var totalSteps: Int = 0 {
		willSet(newTotalSteps) {
			print("About to set totalSteps to \(newTotalSteps)")
		}
		didSet {
			if totalSteps > oldValue {
				print("Added \(totalSteps - oldValue) steps")
			}
		}
	}
}

let stepCounter = StepCounter()
stepCounter.totalSteps = 200
stepCounter.totalSteps = 360
stepCounter.totalSteps = 896

struct SomeStructure {
	static var storedTypeProperty = "Some value"
	static var computedTypeProperty: Int {
		return 1
	}
}

enum SomeEnumeration {
	static var storedTypeProperty = "Some value"
	static var computedTypeProperty: Int {
		return 6
	}
}

class SomeClass {
	static var storedTypeProperty = "Some value"
	static var computedTypeProperty: Int {
		return 27
	}
	class var overrideableComputedTypeProperty: Int {
		return 107
	}
}

print(SomeStructure.storedTypeProperty)
SomeStructure.storedTypeProperty = "Another value"
print(SomeStructure.storedTypeProperty)
print(SomeEnumeration.computedTypeProperty)
print(SomeClass.computedTypeProperty)