9.类和结构体

 class SomeClass {
    // class definition goes here
 }

 struct SomeStructure {
    // structure definition goes here
 }

//结构体
struct Resolution
{
    var width = 0;
    var height = 0;
}

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

// TODO: 实例化
let someResolution = Resolution();
let someVideoMode = VideoMode();

// TODO: 属性操作
var width = someResolution.width;
//someVideoMode.resolution.width = 100;
var width2 = someVideoMode.resolution.width;

// TODO: 结构体类型的成员逐一构造器
var otherResolution = Resolution(width: 30, height: 20);
//【说明】：所有结构体都有一个自动生成的成员逐一构造器，用于初始化新结构体实例中成员的属性。新实例中各个属性的初始值可以通过属性的名称传递到成员逐一构造器之中。类实例没有默认的成员逐一构造器。

//结构体
struct Resolution
{
    var width = 0;
    var height = 0;
}

let hd = Resolution(width: 1920, height: 1080);
var cinema = hd;
cinema.width = 2000;
print("cinema is now  \(cinema.width) pixels wide");  //"cinema is now  2000 pixels wide\n"
print("hd is still \(hd.width) pixels wide");  //"hd is still 1920 pixels wide\n"

 struct Resolution
 {
    var width = 0;
    var height = 0;
 }
 
 class VideoMode
 {
    var resolution = Resolution();
    var interlaced = false;
    var frameRate = 0.0;
    var name: String?;
 }
 
 let tenEighty = VideoMode();
 tenEighty.resolution = Resolution(width: 1920, height: 1080);
 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)");  //"The frameRate property of tenEighty is now 30.0\n"
 
 // TODO: 恒等运算符(等价于（===）和不等价于（!==）)：检测两个常量或者变量是否引用同一个实例
  if (tenEighty === alsoTenEighty)
  {
    print("tenEighty and alsoTenEighty refer to the same Resolution instance.");
  }

 //【说明】：自定义的类和结构体没有对等价运算符进行默认实现，等价运算符通常被称为“相等”运算符（==）与“不等”运算符（!=）。对于自定义类型，Swift 无法判断其是否“相等”，因为“相等”的含义取决于这些自定义类型在代码中所扮演的角色。