ArkTS-Enum&Union&Aliases类型

enum ColorSet { Red, Green, Blue }
let c: ColorSet = ColorSet.Red;

enum ColorSet { White = 0xFF, Grey = 0x7F, Black = 0x00 }
let c: ColorSet = ColorSet.Black;

enum OrderStatus {
  Placed,
  Shipped,
  Delivered,
}

function checkOrderStatus(status: OrderStatus) {
  switch (status) {
    case OrderStatus.Placed:
      console.log('Order has been placed.');
      break;
    case OrderStatus.Shipped:
      console.log('Order has been shipped.');
      break;
    case OrderStatus.Delivered:
      console.log('Order has been delivered.');
      break;
  }
}

const status = OrderStatus.Shipped;
checkOrderStatus(status);

class Cat {
  // ...
}
class Dog {
  // ...
}
class Frog {
  // ...
}
type Animal = Cat | Dog | Frog | number
// Cat、Dog、Frog是一些类型（类或接口）

let animal: Animal = new Cat();
animal = new Frog();
animal = 42;
// 可以将类型为联合类型的变量赋值为任何组成类型的有效值

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
}

type Matrix = number[][];
type Handler = (s: string, no: number) => string;
type Predicate  = (x: T) => boolean;
type NullableObject = Object | null;

type MyNumber = number;
type MyString = string;

type MathOperation = (a: number, b: number) => number;
const add: MathOperation = (a, b) => a + b;
const subtract: MathOperation = (a, b) => a - b;

type List = Array;
const numbersList: List = [1, 2, 3];
const stringsList: List = ['a', 'b', 'c'];