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Possible? Capture and return modified signature #10215

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Possible? Capture and return modified signature#10215
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QuestionAn issue which isn't directly actionable in code

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@unional
Homa Wong (unional)
opened on Aug 8, 2016

TypeScript: 2.0.0

function factorial(num: number): number { ... }

// pfact signature: pfact(num: number): Promise<number>
const pfact = promisify(factorial)

AFAIK it is currently not possible, thus we need to do something like this:
https://github.com/types/npm-bluebird/blob/master/bluebird.d.ts#L333

Is it possible in the future, or it's just a hard limitation that it can't be done?

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  1. yortus commented on Aug 9, 2016

    @yortus
    Troy Gerwien (yortus)
    on Aug 9, 2016
    Contributor

    Would #5453 solve this?

  2. Igorbek commented on Aug 9, 2016

    @Igorbek
    Igor Oleinikov (Igorbek)
    on Aug 9, 2016
    Contributor

    For any given number of parameters it is possible and easy:

    declare function promisify<T, R>(fn: (arg: T) => R): (arg: T) => Promise<R>;
declare function promisify<T1, T2, R>(fn: (arg1: T1, arg2: T2) => R): (arg1: T1, arg2: T2) => Promise<R>;

    However the most general declaration would require #5453 (Troy Gerwien (@yortus) thanks, was looking for it when you replied).

  3. Igorbek commented on Aug 9, 2016

    @Igorbek
    Igor Oleinikov (Igorbek)
    on Aug 9, 2016
    Contributor

    BTW, I wanted to file suggestion/proposal for way more complicated scenarios like that:

    declare function f<T>(arg: T): [T];
const pf = promisify(f); // it won't infer <T>(arg: T) => Promise<T> -- which is sad

  4. Igorbek commented on Aug 11, 2016

    @Igorbek
    Igor Oleinikov (Igorbek)
    on Aug 11, 2016
    Contributor

    Homa Wong (@unional) I described my thoughts on how we could express these types of signatures. Long read :) #10247

  5. unional commented on Aug 12, 2016

    @unional
    Homa Wong (unional)
    on Aug 12, 2016
    ContributorAuthor

    Thanks. I'll check it out

  6. Ryan Cavanaugh (RyanCavanaugh)
    added
    QuestionAn issue which isn't directly actionable in code
    on Aug 15, 2016
  7. Mohamed Hegazy (mhegazy)
    closed this as completedon Sep 20, 2016
  8. microsoft
    locked and limited conversation to collaborators on Jun 19, 2018
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