Type [number,number] is not recognized correctly #12579

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1. aluanhaddad commented on Nov 30, 2016

   

   Aluan Haddad (aluanhaddad)

   on Nov 30, 2016

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   Error message is a bit off putting but I think the behavior is right.
   You can add this to make it work

   interface Array<T> {
     map(f: (x: T) => [T, T]): [T, T][];
   }
   
   type Data = [number, number];
   let a: Data[] = [1, 2, 3, 4, 5].map(v => [v, v + 1]);
2. k8w commented on Nov 30, 2016

   

   Zhongyang Wang (k8w)

   on Nov 30, 2016

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   Shouldn't v=>[v, v+1] be recognized as [number, number] instead of number[][] ?
3. mhegazy commented on Nov 30, 2016

   

   Mohamed Hegazy (mhegazy)

   on Nov 30, 2016

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   Tuple types are only inferred in the presence of a contextual type. e.g. let a: Data = [1, 2]. the issue here is that the contextual type does not flow through map, since the return type position is not a generic argument inference site. issue #11152 is tracking fixing that.

   👍React with 👍1Reacted by Aluan Haddad
4. mhegazy commented on Nov 30, 2016

   

   Mohamed Hegazy (mhegazy)

   on Nov 30, 2016

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   closing in favor of #11152
5. Mohamed Hegazy (mhegazy)

   closed this as completedon Nov 30, 2016
6. Mohamed Hegazy (mhegazy)

   added

   DuplicateAn existing issue was already createdAn existing issue was already created

   on Nov 30, 2016
7. microsoft

   locked and limited conversation to collaborators on Jun 19, 2018