泛型Generics

约束泛型entends

interface IWithLen {
	length: number
}
// extends 约束
function RetLen<T extends IWithLen>(arg: T): T {
	console.log(arg.length)
	return arg
}

泛型在类和接口的使用

// 泛型类
class GenericNumber<T> {
  zeroValue: T;
  add: (x: T, y: T) => T;
}

// 泛型接口
interface KeyPair<T, U> {
	key: T
	value: U
}
let kp1: KeyPair<number, string> = { key: 1, value: "string"}
let kp2:KeyPair<string, number> = {key:'str', value:2}

类型别名，字面量和交叉类型

// 类型别名
type Name = string
type NameResolver = () => string
type NameOrResolver = Name | NameResolver
// 字面量
const strZ: 'name' = 'name'
const number: 1 = 1
/ 交叉类型
interface Iname {
	name: string
}
// 加上去，交叉组合时使用type
type IPerson = Iname & { age: number }
let person: IPerson = { name: '123', age: 23 }

在用到别名或者交叉组合时用type，遇到类和接口用interface