Description
Bug Report
🔎 Search Terms
expando, property assignments, arrow expression, #26368, #44988, #42203
🕗 Version & Regression Information
- This is the behavior in every version I tried since TypeScript 3.1
⏯ Playground Link
Playground link with relevant code
💻 Code
type DescribableFunction = {
description: string;
(someArg: number): boolean;
};
const ok: DescribableFunction = (x: number) => false;
ok.description = 'description';
const ko: DescribableFunction = ((x: number) => false); // error!
// ~~ <-- Property 'description' is missing
ko.description = 'description';🙁 Actual behavior
ko is not recognized as a function capable of having expando properties added to it, while ok is recognized as such.
🙂 Expected behavior
Both ok and ko should behave the same way and allow expando properties as implemented in #26368. I don't know if it's common or not to use parentheses in this situation, but it was surprising to me when I ran into this discrepancy. I see from #44988 and #42203 that sometimes parentheses will disrupt things, so this is presumably an unanticipated use case that may not be important enough for anyone to address.