typescript：您将如何返回具有相同 arguments 但不同类型的新 function 的 ZDBC11CAA5BDA929F77E6FB4DBEDA88

Question

const stringToDate = ( x: string ) => new Date( x )
//    stringToDate: (x: string) => Date

type MapTupleValues<Tuple extends any[], NewValue> = {
    [ index in keyof Tuple ]: NewValue
}

type TestMappedTuple = MapTupleValues<[ a: Date, b: Date ], string>
//   TestMappedTuple = [a: string, b: string]
// works fine

function modifyFn<Fn extends ( ...args: Date[] ) => any> ( fn: Fn ) {
    return ( ...args: MapTupleValues<Parameters<Fn>, string> ): ReturnType<Fn> => {
        //   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error
        //   A rest parameter must be of an array type.

        return fn( ...args.map( x => stringToDate( x ) ) )
    }
}

const daysDifference = ( start: Date, end: Date ) => ( end.getTime() - start.getTime() ) / ( 1000 * 60 * 60 * 24 )
//    daysDifference: (start: Date, end: Date) => number

const modifiedDaysDifference = modifyFn( daysDifference )
//    modifiedDaysDifference: (start: string, end: string) => number

console.log( daysDifference( new Date( '2022-07-29' ), new Date( '2022-08-21' ) ) ) // 23
console.log( modifiedDaysDifference( '2022-07-29', '2022-08-21' ) ) // 23

this seems to be working, even though there is an error in modifyFn
how can I get rid of the error while still getting the same result?

Answer 1

Thanks jcalz

Here's their answer:

const stringToDate = (x: string) => new Date(x)
//    stringToDate: (x: string) => Date

type MapTupleValues<T extends any[], V> = Extract<{
    [I in keyof T]: V
}, any[]>

type TestMappedTuple = MapTupleValues<[a: Date, b: Date], string>
//   TestMappedTuple = [a: string, b: string]
// works fine

function modifyFn<Fn extends (...args: Date[]) => any>(fn: Fn) {
    return (...args: MapTupleValues<Parameters<Fn>, string>): ReturnType<Fn> => {
        return fn(...args.map(x => stringToDate(x)))
    }
}

const daysDifference = (start: Date, end: Date) => (end.getTime() - start.getTime()) / (1000 * 60 * 60 * 24)
//    daysDifference: (start: Date, end: Date) => number

const modifiedDaysDifference = modifyFn(daysDifference)
//    modifiedDaysDifference: (start: string, end: string) => number

console.log(daysDifference(new Date('2022-07-29'), new Date('2022-08-21'))) // 23
console.log(modifiedDaysDifference('2022-07-29', '2022-08-21')) // 23