TypeScript mapped type for proxy

Asked Jul 22 '17 at 19:04

Active Jul 22 '17 at 19:15

Viewed 609 times

I want to achieve a conceptually simple thing: transform a map of functions that return any (or, for the sake of the example, number) to a map of functions that return void, while conserving the other type information.

Expressed in code, I would like to do something like this:

type Source = {
    [fn: string]: (...args: any[]) => number
}

type Output = {
    [fn: string]: (...args: any[]) => void
}

function proxy(source: Source): Output {
    // Do something with the source...
    return source
}

const result = proxy({
    answerToLifeTheUniverseAndEverything: (question?: string): number => 42
})

// Should work, and the method should be suggested as part of the auto-completion.
result.answerToLifeTheUniverseAndEverything()

// The compiler should complain.
result.answerToLifeTheUniverseAndEverything(false)

edited Jul 22 '17 at 19:15

asked Jul 22 '17 at 19:04

DanielM

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Why would the compiler complain in your second call? – Rodris Jul 23 '17 at 12:44
Because the function expects a string, but in the second call I'm providing a boolean. – DanielM Jul 23 '17 at 12:53
Did you read the article on advanced types, specifically the section about "mapped types" here? https://www.typescriptlang.org/docs/handbook/advanced-types.html – Alex Lockwood Sep 01 '17 at 16:49
I did, but still I fail to see how to apply the knowledge there to the case in hand. – DanielM Sep 03 '17 at 18:20

TypeScript mapped type for proxy

0 Answers0