泛型 (opens new window)

带参数的类型

function identity<Type>(arg: Type): Type {
  return arg;
}

===================================类型声明==赋值
let myIdentity: <Type>(arg: Type) => Type = identity;

let output = identity<string>("myString");

let output = identity("myString");


function loggingIdentity<Type>(arg: Type[]): Type[] {
  console.log(arg.length);
  return arg;
}

function loggingIdentity<Type>(arg: Array<Type>): Array<Type> {
  console.log(arg.length); // Array has a .length, so no more error
  return arg;
}

我们还可以将泛型类型写为对象文字类型的调用签名：

function identity<Type>(arg: Type): Type {
  return arg;
}

let myIdentity: { <Type>(arg: Type): Type } = identity;

泛型接口

function identity<Type>(arg: Type): Type {
  return arg;
}

let myIdentity: { <Type>(arg: Type): Type } = identity;

// 用泛型接口重写

interface GenericIdentityFn {
  <Type>(arg: Type): Type;
}


let myIdentity: GenericIdentityFn = identity;

// 更好的方式
interface GenericIdentityFn<Type> {
  (arg: Type): Type;
}

let myIdentity: GenericIdentityFn<number> = identity;

泛型类

泛型类仅对他的实例属性使用泛型

class GenericNumber<NumType> {
  zeroValue: NumType;
  add: (x: NumType, y: NumType) => NumType;
}

实例一
let myGenericNumber = new GenericNumber<number>();
myGenericNumber.zeroValue = 0;
myGenericNumber.add = function (x, y) {
  return x + y;
};


实例二

let stringNumeric = new GenericNumber<string>();
stringNumeric.zeroValue = "";
stringNumeric.add = function (x, y) {
  return x + y;
};

console.log(stringNumeric.add(stringNumeric.zeroValue, "test"));

泛型约束Type extends Lengthwise

interface Lengthwise {
  length: number;
}

function loggingIdentity<Type extends Lengthwise>(arg: Type): Type {
  console.log(arg.length); // Now we know it has a .length property, so no more error
  return arg;
}

在泛型中使用类型参数

function getProperty<Type, Key extends keyof Type>(obj: Type, key: Key) {
  return obj[key];
}

let x = { a: 1, b: 2, c: 3, d: 4 };

getProperty(x, "a");
getProperty(x, "m");

在泛型中使用类类型

使用泛型在TypeScript中创建工厂时，有必要通过其构造函数来引用类类型

class BeeKeeper {
  hasMask: boolean;
}

class ZooKeeper {
  nametag: string;
}

class Animal {
  numLegs: number;
}

class Bee extends Animal {
  keeper: BeeKeeper;
}

class Lion extends Animal {
  keeper: ZooKeeper;
}

function createInstance<A extends Animal>(c: new () => A): A {
  return new c();
}

createInstance(Lion).keeper.nametag;
createInstance(Bee).keeper.hasMask;