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typescript - 具有重载函数的类型推断

问题描述

考虑以下重载函数：

function foo(arg1: string, cb: (err: Error|null, res: string) => void): void
function foo(arg1: string, arg2: string, cb: (err: Error|null, res: string) => void): void

我想promisify使用这样的功能。但默认实现返回无效类型。

当它返回时

(arg1: string, arg2: string) => Promise<{}>

我希望它会回来

{
   (arg1: string): Promise<string>;
   (arg1: string, arg2: string): Promise<string>;
}

考虑到这一点，我想修正打字问题。我设法使用以下方法覆盖了该特定原型：

export type Callback<T> = (err: Error | null, reply: T) => void;
export type Promisify<T> =

    T extends {
        (arg1: infer T1, cb?:  Callback<infer U>): void;
        (arg1: infer P1, arg2: infer P2, cb?:  Callback<infer U2>): void;
    } ? {
        (arg1: T1): Promise<U>;
        (arg1: P1, arg2: P2): Promise<U2>;
    } :

    T extends (cb?:  Callback<infer U>) => void ? () => Promise<U> :
    T extends (arg1: infer T1, cb?:  Callback<infer P>) => void ? (arg1: T1) => Promise<P> :
    T extends (arg1: infer T1, arg2: infer T2, cb?:  Callback<infer U>) => void ? (arg1: T1, arg2: T2) => Promise<U> :
    T extends (arg1: infer T1, arg2: infer T2, arg3: infer T3, cb?:  Callback<infer U>) => void ? (arg1: T1, arg2: T2, arg3: T3) => Promise<U> :
    T extends (arg1: infer T1, arg2: infer T2, arg3: infer T3, arg4: infer T4, cb?:  Callback<infer U>) => void ? (arg1: T1, arg2: T2, arg3: T3, arg4: T4) => Promise<U> :
    T;

但这需要我专门列出所有潜在的方法重载。

有没有办法一次转换所有方法重载，类似于我们如何转换对象属性？

标签： typescript

解决方案

我们可以在剩余参数和展开表达式中使用元组的 3.0 特性来获得重载参数的联合，但我们需要为函数具有的每个重载数量添加一个案例：

export type GetOverloadArgs<T> = 
    T extends { (...o: infer U) : void, (...o: infer U2) : void, (...o: infer U3) : void   } ? U | U2 | U3:
    T extends { (...o: infer U) : void, (...o: infer U2) : void  } ? U | U2 :
    T extends { (...o: infer U) : void } ? U : never

所以例如对于 foo

type fooParams = GetOverloadArgs<typeof foo> 
// will be 
type fooParams = [string, (err: Error | null, res: string) => void] | [string, string, (err: Error | null, res: string) => void]

由此我们可以使用类似于您的类型Promisify为 union 中的每个参数集创建一个函数：

export type PromisifyOne<T extends any[]> =
    T extends [Callback<infer U>?] ? () => Promise<U> :
    T extends [infer T1, Callback<infer P>] ? (arg1: T1) => Promise<P> :
    T extends [infer T1, infer T2, Callback<infer U>?] ? (arg1: T1, arg2: T2) => Promise<U> :
    T extends [infer T1, infer T2, infer T3, Callback<infer U>?]? (arg1: T1, arg2: T2, arg3: T3) => Promise<U> :
    T extends [infer T1, infer T2, infer T3, infer T4, Callback<infer U>?] ? (arg1: T1, arg2: T2, arg3: T3, arg4: T4) => Promise<U> :
    T;

并且使用条件类型的分配行为，我们可以创建所有重载的联合：

export type Promisify<T> =PromisifyOne<GetOverloadArgs<T>> 
export type Promisify<T> =PromisifyOne<GetOverloadArgs<T>> 
type fooOverloadUnion = Promisify<typeof foo>
// Same as 
type fooOverloadUnion = ((arg1: string) => Promise<string>) | ((arg1: string, arg2: string) => Promise<string>)

为了使它再次可调用，我们可以使用将联合转换为交集，使用UnionToIntersection，最终结果为：

export type Callback<T> = (err: Error | null, reply: T) => void;
export type PromisifyOne<T extends any[]> =
    T extends [Callback<infer U>?] ? () => Promise<U> :
    T extends [infer T1, Callback<infer P>?] ? (arg1: T1) => Promise<P> :
    T extends [infer T1, infer T2, Callback<infer U>?] ? (arg1: T1, arg2: T2) => Promise<U> :
    T extends [infer T1, infer T2, infer T3, Callback<infer U>?]? (arg1: T1, arg2: T2, arg3: T3) => Promise<U> :
    T extends [infer T1, infer T2, infer T3, infer T4, Callback<infer U>?] ? (arg1: T1, arg2: T2, arg3: T3, arg4: T4) => Promise<U> :
    T;

export type GetOverloadArgs<T> = 
    T extends { (...o: infer U) : void, (...o: infer U2) : void, (...o: infer U3) : void   } ? U | U2 | U3:
    T extends { (...o: infer U) : void, (...o: infer U2) : void  } ? U | U2 :
    T extends { (...o: infer U) : void } ? U : never

type UnionToIntersection<U> = (U extends any ? (k: U)=>void : never) extends ((k: infer I)=>void) ? I : never
export type Promisify<T> =  UnionToIntersection<PromisifyOne<GetOverloadArgs<T>>>

// Sample
declare function foo(arg1: string, cb: (err: Error|null, res: string) => void): void
declare function foo(arg1: string, arg2: string, cb: (err: Error|null, res: string) => void): void

declare const  fooPromise: Promisify<typeof foo>
let r = fooPromise("")
let r2 = fooPromise("", "")

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