Description

ZpdDG4gta (zpdDG4gta8XKpMCd)

opened on Nov 20, 2015

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type Foo = (one: string) => number;

function fooOver() : Foo {
    return one => parseInt(one); // <-- one is string
}

type Bar = <a>(one: string) => a;

function barOver() : Bar {
    return one => parseInt(one); // <-- one is god knows what
}

Activity

1. Ryan Cavanaugh (RyanCavanaugh)

   added

   BugA bug in TypeScriptA bug in TypeScript

   on Nov 20, 2015
2. RyanCavanaugh commented on Nov 20, 2015

   

   Ryan Cavanaugh (RyanCavanaugh)

   on Nov 20, 2015

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   Technically this is according to per spec (I know, your favorite response), but I think we should do better here.

   Section 4.2.3 (https://github.com/Microsoft/TypeScript/blob/master/doc/spec.md#423-contextually-typed-expressions) says

   In the body of a function expression or arrow function that has no return type annotation, if the function expression or arrow function is contextually typed by a function type with exactly one call signature, and if that call signature is non-generic, return expressions are contextually typed by the return type of that call signature.

   We already said that we should contextually type parameters when type annotations are present somewhere --- no reason we shouldn't contextually type using the non-generic parameter positions or non-generic return positions.
3. Ryan Cavanaugh (RyanCavanaugh)

   added

   SpecIssues related to the TypeScript language specificationIssues related to the TypeScript language specification

   on Nov 20, 2015
4. Anders Hejlsberg (ahejlsberg)

   added a commit that references this issue on Dec 3, 2015

   Merge pull request #5737 from Microsoft/unionIntersectionTypeInference

   b022893
5. ahejlsberg commented on Dec 7, 2015

   

   Anders Hejlsberg (ahejlsberg)

   on Dec 7, 2015

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   Ryan Cavanaugh (@RyanCavanaugh) There is no easy way to tell whether a particular type references a type parameter and I honestly think that we either contextually type all parameters or none. Anything in between just gets even more confusing.
6. Mohamed Hegazy (mhegazy)

   added

   SuggestionAn idea for TypeScriptAn idea for TypeScript

   In DiscussionNot yet reached consensusNot yet reached consensus

   and removed

   BugA bug in TypeScriptA bug in TypeScript

   SpecIssues related to the TypeScript language specificationIssues related to the TypeScript language specification

   on Dec 8, 2015
7. Daniel Rosenwasser (DanielRosenwasser)

   changed the title [-]another inferrence strangeness[/-] [+]Make functions generic when contextually typed by a generic signature[/+] on Aug 21, 2016
8. Ryan Cavanaugh (RyanCavanaugh)

   closed this as completedon Jul 29, 2019

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