Inferring types: curried vs not curried #15005

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1. PyroVortex commented on Apr 4, 2017

   

   PyroVortex

   on Apr 4, 2017

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   Type inference will also work with this declaration:

   declare function props<P1 extends string, P2 extends string, O extends {[K in P1 | P2]: any}>
     (ps: [P1, P2], obj: O): [O[P1], O[P2]];

   In your first example, the mapped types for obj are additional inference sites for P1 and P2, which results in them being both inferred as 'a' | 'b'. In the curried case, P1 and P2 are fixed as 'a' and 'b', respectively, when the second function gets called, and therefore limit what each of the two intersected types matches.

   👍React with 👍2Reacted by Aluan Haddad and Alex
2. wclr commented on Apr 5, 2017

   

   Alex (wclr)

   on Apr 5, 2017

   Last edited by wclr

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   PyroVortex
   Is it possible for this case to limit ps tuple size to 2? Or prohibit props that are not in obj

   So it wouldn't allow:

   // should be an error, as 'whatever' is not in {a: 1, b: '2'}`
   props(['a', 'b', 'whatever'])({a: 1, b: '2'})[0] 
3. Ryan Cavanaugh (RyanCavanaugh)

   added

   Needs InvestigationThis issue needs a team member to investigate its status.This issue needs a team member to investigate its status.

   on May 24, 2017
4. raveclassic commented on Oct 17, 2018

   

   Kirill Agalakov (raveclassic)

   on Oct 17, 2018

   Last edited by raveclassic

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   I run into similar problem:

   declare const a: { cb: (arg: number) => void }
   
   declare function test1<T>(a: T, b: T): void;
   test1(a, { cb(arg) { } }) // parameter 'arg' implicitly has an 'any' type
   
   declare function test2<T>(a: T, b: () => T): void;
   test2(a, () => ({ cb(arg) { } })) // parameter 'arg' implicitly has an 'any' type
   
   declare function test3<T>(a: T): (b: T) => void // curried
   test3(a)({ cb(arg) { } }) // (parameter) arg: number
   
   declare function test4<T>(a: T): (b: () => T) => void // curried
   test4(a)(() => ({ cb(arg) { } })) // (parameter) arg: number

   Looks like there're some related issues: #23429, #22715 #25092

   👍React with 👍1Reacted by Sergey Cherepanov
5. Kirill Agalakov (raveclassic)

   added 2 commits that reference this issue on Oct 17, 2018

   chore(react-kit): make withRX curried for better type inference micro…

   ...

   2380110

   feat(react-kit): accept defaultProps in withrx selector result (#83)

   ...

   471706f
6. Ryan Cavanaugh (RyanCavanaugh)

   added

   QuestionAn issue which isn't directly actionable in codeAn issue which isn't directly actionable in code

   and removed

   Needs InvestigationThis issue needs a team member to investigate its status.This issue needs a team member to investigate its status.

   on Sep 16, 2019
7. TypeScript Bot (typescript-bot)

   closed this as completedon Sep 21, 2019
8. typescript-bot commented on Sep 21, 2019

   

   TypeScript Bot (typescript-bot)

   on Sep 21, 2019

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   This issue has been marked as 'Question' and has seen no recent activity. It has been automatically closed for house-keeping purposes. If you're still waiting on a response, questions are usually better suited to stackoverflow.

   😕React with 😕1Reacted by Kirill Agalakov
9. microsoft

   locked as resolved and limited conversation to collaborators on Oct 21, 2025