（一）ArkTS语言——申明与类型

官网地址：
https://developer.huawei.com/consumer/cn/doc/harmonyos-guides-V5/introduction-to-arkts-V5

// 1.1声明

//变量声明
let name:string = 'hello';
// 赋值
name = 'hello word';
//常量申明
const id:string = 'abc'

// 1.2类型

//number
let n1 = 3.14;
let n2 = .5;
let n3 = 1e2;
//boolean
let flag: boolean = true;
flag = true;
//string
let s1 = 's1';
let s2 = "s2";
let s3 = `${s2} is  not s3`;
//void
class Case<T>{
  //...
}
let instance: Case<void>;
//Object
//任何值，都可以直接被赋给Object
//array
let names:string [] = ['A','B','C'];
//enum
enum ColorSet {Red, Green, Blue};
let c: ColorSet = ColorSet.Red;
//union
class Cat { sleep () {}; meow () {} }
class Dog { sleep () {}; bark () {} }
class Frog { sleep () {}; leap () {} }

type Animal = Cat | Dog | Frog;

function foo(animal: Animal) {
  if (animal instanceof Frog) {
    animal.leap();  // animal在这里是Frog类型
  }
  animal.sleep(); // Animal具有sleep方法
}
//Aliases
//Aliases类型为匿名类型提供名称