Swift Lazy, Computed, Observers Properties

//1. Lazy Stored Properties

class DataImporter {
    var fileName = "data.txt"
}

class DataManager {
    lazy var importer = DataImporter()
    var data = [String]()
}



var m = DataManager()
m.data.append("data 1 ")
m.data.append("data 2 ")
//m.importer has not yet been created.
print( m.importer.fileName )
//m.importer has been created now.









//2. Computed Properties

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 tmpx = origin.x + size.width/2
            let tmpy = origin.y + size.height/2
            return Point(x:tmpx,y:tmpy)

        }

        // set {
        //     origin.x = newValue.x - size.width/2
        //     origin.y = newValue.y - size.height/2
        // }

     

        // renaming newCenter as newValue
        set ( newCenter ){
            origin.x = newCenter.x - size.width/2
            origin.y = newCenter.y - size.height/2
        }
    }
}



var r = Rect(origin:Point(x:10,y:10), size:Size(width:20,height:20))
print( r.center)



// 3. setter, getter

class Test {
   var _power : Double = 0.0
   var power : Double {
        get {
            return _power
        }

        set (newValue){
            _power = newValue
        }
    }
}







/* 4.Property Objservers


willSet is called just before the value is stored.
didSet is called immediately after the new value is stored.”

*/



class Sample {
    var force : Int = 0 {
        willSet(newV){
            print("\(force) -> \(newV)")
        }

        didSet {
            print("\(oldValue) -> \(force)")
        }
    }
}


var s = Sample()
print(s.force)
s.force = 12
print(s.force)