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No easy way to convince TypeScript a variable has been initialized. #12855

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No easy way to convince TypeScript a variable has been initialized.#12855
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@DanielRosenwasser
Daniel Rosenwasser (DanielRosenwasser)
opened on Dec 12, 2016

Reported by Yehuda Katz (@wycats). Compile this under strictNullChecks and noImplicitAny.

declare function someAbstraction(x: any): any;

let x: string;

someAbstraction(() => {
  x = "hello";
});

// All of the following are errors.
x;
x as any;
x!;

I'd argue that both type assertions should be able to signal to the type system that the variable has been initialized.

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Daniel Rosenwasser (DanielRosenwasser)
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BugA bug in TypeScript
on Dec 12, 2016

RyanCavanaugh commented on Dec 12, 2016

@RyanCavanaugh
Ryan Cavanaugh (RyanCavanaugh)
on Dec 12, 2016
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Duplicate #11463

Mohamed Hegazy (mhegazy)
added
DuplicateAn existing issue was already created
and removed
BugA bug in TypeScript
on Dec 12, 2016

mhegazy commented on Dec 13, 2016

@mhegazy
Mohamed Hegazy (mhegazy)
on Dec 13, 2016
Contributor

declaring x as string | undefined should make these all work though.

Mohamed Hegazy (mhegazy)
closed this as completedon Dec 13, 2016
microsoft
locked and limited conversation to collaborators on Jun 19, 2018
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