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Broken type inference for union of function and object #59573
Description
🔎 Search Terms
function union infer
🕗 Version & Regression Information
- This is the behavior in every version I tried, and I reviewed the FAQ for entries about Structural vs Instantiation-Based Inference
⏯ Playground Link
💻 Code
type FunctionalComponent<T> = (props: T) => string;
const test = <T>(props: { values: T[], selected: T }) => {
const {values, selected} = props;
return `test: ${values}, selected: ${selected}`;
};
const ComponentPassthrough = <T>(comp: FunctionalComponent<T>): FunctionalComponent<T> => comp;
const ComponentAugment = <T>(comp: FunctionalComponent<T>): FunctionalComponent<T> & { id: number } => Object.assign(comp, { id: 10 });
const a = ComponentPassthrough(test);
const b = ComponentAugment(test);🙁 Actual behavior
Typescript cannot infer/passthrough the type parameter in ComponentAugment
🙂 Expected behavior
It should resolve ComponentAugment the same way it does with ComponentPassthrough, but with the added id property in this case. The expected type of b in this example should be:
(<T>(props: {
values: T[];
selected: T;
}) => string) & { id: number }Additional information about the issue
No response
Activity
jcalz commentedon Aug 9, 2024
Essentially a duplicate of #49505. TS has quite limited support for higher order function type inference; it's implemented at #30215 and mentions the very specific circumstances in which you can expect it to work. As soon as you do something like add that intersection, it stops working.
typescript-bot commentedon Aug 12, 2024
This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.