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Unexpected union type between generic and non-generic function #12970

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Unexpected union type between generic and non-generic function#12970
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Description

@gcnew
Marin Marinov (gcnew)
opened on Dec 16, 2016

TypeScript Version: nightly (2.2.0)

Code

function id<T>(x: T): T {
    return x;
}

function stringId(x: string): string {
    return x;
}

function numberId(x: number): number {
    return x;
}

// OK: ((x: string) => string) | ((x: number) => number)
const f = true ? numberId : stringId;

// Actual: <T>(x: T) => T
// Expected: (x: string) => string
const g = true ? id : stringId;

Expected behavior:
Union between a function and a generic function should yield the most specific type, not the most general one.

Activity

  1. JsonFreeman commented on Mar 22, 2017

    @JsonFreeman
    Jason Freeman (JsonFreeman)
    on Mar 22, 2017
    Contributor

    I agree with the expected behavior. I also wonder if it would be reasonable to not collapse the union and keep both constituents.

  2. Ryan Cavanaugh (RyanCavanaugh)
    added
    Needs InvestigationThis issue needs a team member to investigate its status.
    on May 24, 2017

  3. gcnew commented on Jun 9, 2017

    @gcnew
    Marin Marinov (gcnew)
    on Jun 9, 2017
    ContributorAuthor

    Fixed by #16368

  4. Marin Marinov (gcnew)
    closed this as completedon Jul 7, 2017
  5. microsoft
    locked and limited conversation to collaborators on Jun 19, 2018
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