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Another narrowing bug with {} #18413
Description
TypeScript Version: playground
Code
type unknown = {} | undefined | null | void;
interface Dict {
[key: string]: unknown;
}
function isDict(value: any): value is Dict {
return value !== null && value !== undefined;
}
function any(): any {
}
let notSure: unknown = any();
if (isDict(notSure)) {
notSure['foo']; // <- turn on strict mode to see error, `notSure` is `{}`
}Expected behavior:
notSure is Dict after the narrowing
Actual behavior:
notSure is {} after the narrowing
Activity
chancancode commentedon Sep 12, 2017
This is only a problem with
{}involved – the definition suggested here worksRyanCavanaugh commentedon Sep 12, 2017
A union with
{ }in it will eagerly collapse to{ }as soon as it's examined by the type system; a union like this should never be written down on purpose. Did you meanunknown = object | undefined | null | void?chancancode commentedon Sep 12, 2017
We have switched to
unknown = object | number | string | boolean | symbol | undefined | null | voidas per #18196, just thought we would report this in case it is a bug that is not already known.mhegazy commentedon Oct 3, 2017
Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.