结合范型使用函数重载

TypeScript 允许我们声明函数重载。这对于文档 + 类型安全来说很实用：

export interface ResourceData {
  id: string;
  name: string;
  data: any;
}

export function getResource(path: string): ResourceData;
export function getResource(path: string[]): ResourceData[];
export function getResource(path: string | string[]): any {
  return {} as any;
}

const resource = getResource("a.json");// ResourceData
const resources = getResource(["b.json", "c.json"]); // ResourceData[]

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不仅如此，函数重载也可以和范型结合起来，来实现更加强大的功能：

function compose<Input, FirstArg>(
  func: (input: Input) => FirstArg
): (input: Input) => FirstArg

function compose<Input, FirstArg, SecondArg>(
  func: (input: Input) => FirstArg, 
  func2: (input: Input) => SecondArg
): (input: Input) => SecondArg

function compose<Input, FirstArg, SecondArg, ThirdArg>(
  func: (input: Input) => FirstArg, 
  func2: (input: Input) => SecondArg, 
  func3: (input: SecondArg) => ThirdArg
): (input: Input) => ThirdArg
function compose(...args: any[]){
  return {} as any
}

const addOne = (a: number) => {
  return a + 1;
}
const numToString = (a: number) => {
  return a.toString();
}
const stringToNum = (a: string) => {
  return parseInt(a);
}

const addOneToString = compose(addOne, numToString, stringToNum)

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