TypeScript应用 极速上手（18）

1、自定义泛型

class MyArray<T>{
    data:T[] = []
    add(t:T){
        this.data.push(t)
    }
    print(){
        console.log(this.data)
    }

   //MyArray<number>.map<string>(f: (v: number) => string): string[]
   //定义一个泛型方法
   //U:未知的返回类型
   //T:输入参数的类型
    map<U>(f:(v:T) => U):U[]{
        return this.data.map(f)
    }
}

const a = new MyArray<number>()
a.add(1)
a.add(3)
a.add(5)
console.log(a.map(v=>v.toExponential())) 、 ["1e+0", "3e+0", "5e+0"]

2、约束T的类型范围

interface HasWeight {
    weight:number
}

class MyArray<T extends HasWeight> {
    data:T[] = []
    add(t:T){
        this.data.push(t)
    }
    map<U>(f:(v:T) => U):U[]{
        return this.data.map(f)
    }
    print(){
        console.log(this.data)
    }

    sortByWeight(){
        this.data.sort((a,b) => a.weight - b.weight)
    }
}

class WeightNumber {
    constructor(public weight:number){}
}
const a = new MyArray<WeightNumber>()
a.add(new WeightNumber(33))
a.add(new WeightNumber(45))
a.add(new WeightNumber(76))
a.sortByWeight()
console.log(a)
/* 
//输出结果：
MyArray: {
  "data": [
    {
      "weight": 33
    },
    {
      "weight": 45
    },
    {
      "weight": 76
    }
  ]
} 
*/