基础使用：

    1. // 泛型
    2. function echo<T>(arg: T): T {
    3.   return arg
    4. }
    5. const result = echo(123)
    7. // 定义占位符<T,U> 然后去使用
    8. function swap<T, U>(tuple: [T, U]): [U, T] {
    9.   return [tuple[1], tuple[0]]
    10. }

    约束泛型：extends

    1. interface IWithLength {
    2.   length: number
    3. }
    5. function echoWithLength<T extends IWithLength>(arg: T): T {
    6.   console.log(arg.length)
    7.   return arg
    8. }
    10. const echoLength = echoWithLength({ a: 1, length: 1 })
    11. const strLength = echoWithLength('1231')
    12. const arrLength = echoWithLength([1,2])
    13. //const numLength = echoWithLength(123) //报错了

    类的泛型

    1. class Queue<T>{
    2.     private list = []
    3.   push(item:T){
    4.         return this.list.push(item)
    5.   }
    6.   pop():T{
    7.       return this.list.shift()
    8.   }
    9. }
    10.   const queue1 = new Queue<number>()
    11.   queue1.push(1)
    12.   console.log(queue1.pop().toFixed())
    14.   const queue2 = new Queue<string>()
    15.   queue2.push('123asd')
    16.   console.log(queue2.pop().length)

    接口泛型

    1. interface keyPair<T, U> {
    2.   key: T,
    3.   value: U
    4. }
    6. let kp1: keyPair<string, number> = { key: 'str', value: 1 }
    7. let kp2: keyPair<number, string> = { key: 123, value: "" }
    9. let arr1: number[] = [2, 3, 4]
    10. let arr2: Array<number> = [2, 3]
    16. interface Iplus {
    17.   (num1: number, num2: number): number
    18. }
    20. function plus(num1: number, num2: number): number {
    21.   return num1 + num2
    22. }
    24. const num3: Iplus = plus
    30. interface same<T> {
    31.   (num1: T, num2: T): T
    32. }
    34. function add(num1: number, num2: number): number {
    35.   return num1 + num2
    36. }
    38. function connect(num1: string, num2: string): string {
    39.   return num1 + num2
    40. }
    42. const a:same<number> = add
    43. const b:same<string> = connect