Microsoft/TypeScript
Ver no GitHubTypeScript can't infer type of default parameters
Open
#59.643 aberto em 15 de ago. de 2024
Domain: check: Type InferenceHelp WantedPossible Improvement
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Description
🔎 Search Terms
infer default parameters function wrapper function factory
🕗 Version & Regression Information
- This is the behavior in every version I tried, and I reviewed the FAQ
- I tried down to version 4.0.3 (since in the earlier version
Generatortype is not generic)
- I tried down to version 4.0.3 (since in the earlier version
⏯ Playground Link
💻 Code
declare function fnDerive<A extends unknown[], R>(
fn: (...args: A) => Generator<unknown, R>,
): unknown /** mocked return */;
fnDerive(function *(a = 0, b = '') {
console.log({
a,
// ^?
b
// ^?
});
});
🙁 Actual behavior
The type of a and b is unknown.
🙂 Expected behavior
The type of a and b should be number and string
Additional information about the issue
I was working with a library gensync when I hit this issue, and I extracted the minimum reproduction out of it.
Note that if I don't use default parameters, typescript can infer the a and b types correctly:
declare function fnDerive<A extends unknown[], R>(
fn: (...args: A) => Generator<unknown, R>,
): unknown /** mocked return */;
fnDerive(function *(a?: number | undefined, b?: string | undefined) {
console.log({
a,
// ^?
b
// ^?
});
a ??= 0;
b ??= '';
console.log({
a,
// ^?
b
// ^?
});
});