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Incorrect typecheck on generic Promise<T> with inheritance #15564

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MichalLytek opened this issue May 3, 2017 · 1 comment
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Incorrect typecheck on generic Promise<T> with inheritance #15564

MichalLytek opened this issue May 3, 2017 · 1 comment
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@MichalLytek
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TypeScript Version: 2.3.2

Code

class A {
    a: number;
}

class Aplus extends A {
    plus = () => true;
}

function newAplusAsync(): Promise<Aplus> {
    return Promise.resolve(new A());
}

(async () => {
    const aplus = await newAplusAsync();
    console.log(aplus.plus());
})();

Expected behavior:
Compiler error: Type 'Promise<A>' is not assignable to type 'Promise<Aplus>'

Actual behavior:
Runtime error: aplus.plus is not a function​​

@mhegazy
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mhegazy commented May 3, 2017

Should be fixed by #15104, fix should be available today in typescript@next.

@mhegazy mhegazy added the Fixed A PR has been merged for this issue label May 3, 2017
@mhegazy mhegazy added this to the TypeScript 2.4 milestone May 3, 2017
@mhegazy mhegazy closed this as completed May 3, 2017
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