typescript - Typescript中两个函数的联合类型

Question

我有一种情况，我有一个类型，它是两个函数的联合，这两个函数的一个参数的类型是文字值。归结为一个最小的例子，它本质上是这样的:

type FetchMini = (id: number, representation: 'mini') => MiniUser;
type FetchFull = (id: number, representation: 'full') => FullUser;

function f(fetchUser: FetchMini | FetchFull) {
  fetchUser(2, 'mini');
  fetchUser(2, 'full');
}

这两个调用都使编译器失败并显示消息:

Cannot invoke an expression whose type lacks a call signature. Type 'FetchMini | FetchFull' has no compatible call signatures.`

我认为我了解发生这种情况的原因，(...我认为)但我能做些什么呢？

这是一个类似的问题，但没有得到答案:Union of functions is not callable even with parameters that meet each function's constraints

Answer 1

您的 fetchUser() 本质上是一个重载函数，它接受两者 mini 和 full，因此应该是交集类型，而不是并集。

type MiniUser = { name: string }
type FullUser = { firstName: string, lastName: string, age: number }

type FetchMini = (id: number, representation: 'mini') => MiniUser;
type FetchFull = (id: number, representation: 'full') => FullUser;
type FetchBoth = FetchMini&FetchFull

function f(fetchUser: FetchBoth) {
    fetchUser(2, 'mini');
    fetchUser(2, 'full');
}

function fetchBoth(id: number, representation: 'mini'): MiniUser
function fetchBoth(id: number, representation: 'full'): FullUser
function fetchBoth(id: number, representation: 'mini' | 'full') {
    if (representation==='mini')
        return { name: 'Mini' }
    if (representation==='full')
        return { firstName: 'Full', lastName: 'User', age: 20 }
}
f(fetchBoth)

PlayGround

根据经验，当您声明一个接受两种类型 A 和 B args 的函数时，该函数应该是& -打字。