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"...args: infer" on an overloaded function chooses only one function head #26136
Description
Activity
Closing as duplicate of Brian Terlson (@bterlson)'s #26132
Mike North (@mike-north) is this a duplicate, though? #26132 doesn't have overloads, and arguments list inference of
fngives something similar to what you request here:// sample from #26132 type Rec = { foo: (a: string, b: number) => void, bar: (b: boolean, c: RegExp) => void, } type Parameters<T> = T extends (...args: infer U) => any ? U : never; declare var fn: <K extends keyof Rec>(e: K, ...args: Parameters<Rec[K]>) => void; // test parameter extraction type test = Parameters<typeof fn>; // type test = ["foo" | "bar", ...(string | number | boolean | RegExp)[]]
Good catch, I must have read your issue too quickly. Maybe this should be un-tagged as duplicate
Reacted by Brian TerlsonDiscussed for a while yesterday. This looks reasonably straightforward if you're just capturing the entire parameter list into a single spread, but quickly turns into a bunch of really complicated questions once you do anything else
- What would the behavior of
type Args<F> = F extends (n: number, ...args: infer T) => any ? T : never;be? Would it be sound to just capture the matching overloads, or not? - What happens when you put
Tinto a different argument list? Potentially a combinatorially explosive expansion in to overloads? - More problems I can't recall at the moment
Overall too complex unless there are some important use cases that appear.
Reacted by Mike North- What would the behavior of
Ryan Cavanaugh (@RyanCavanaugh)
some example like
Function.prototype.call
Function.prototype.apply
Function.prototype.bind
TypeScript Version: 3.1.0-dev.20180801
Search Terms: overload, infer, function heads, tuple, rest parameter
Code
Expected behavior:
Ideally, I would hope for the typeof
xto bealthough not entirely correct, I would even take a type wide enough to accomodate both function heads.
Actual behavior:
The type of x ends up being
Playground Link: https://www.typescriptlang.org/play/#src=interface%20Foo%20%7B%0D%0A%20%20(a%3A%20string%2C%20b%3A%20number%2C%20c%3A%20boolean)%3A%20void%3B%0D%0A%20%20(a%3A%20number%2C%20b%3A%20string%2C%20c%3A%20boolean)%3A%20void%3B%0D%0A%7D%0D%0A%0D%0Atype%20Args%3CF%3E%20%3D%20F%20extends%20(...args%3A%20infer%20T)%20%3D%3E%20any%20%3F%20T%20%3A%20never%3B%0D%0A%0D%0Alet%20x%3A%20Args%3CFoo%3E%20%3D%20%5B42%2C%20'hello%20world'%2C%20true%5D%3B%20%2F%2F%20%E2%9C%85%0D%0Ax%20%3D%20%5B'hello%20world'%2C%2042%2C%20true%5D%3B%20%2F%2F%20%F0%9F%92%A5
Related Issues: #24897, #5453 (maybe)