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Mapped type indexed access issue #47368
Description
Bug Report
An indexed access type { [P in K]: E }[X] should be assignable to an instantiation of E with X substituted for P.
This issue was originally reported here.
🔎 Search Terms
Mapped type indexed access.
🕗 Version & Regression Information
Nightly build
⏯ Playground Link
Playground link with relevant code
💻 Code
type ArgMap = { a: number, b: string };
type Func<K extends keyof ArgMap> = (x: ArgMap[K]) => void;
type Funcs = { [K in keyof ArgMap]: Func<K> };
function f1<K extends keyof ArgMap>(funcs: Funcs, key: K, arg: ArgMap[K]) {
funcs[key](arg);
}
function f2<K extends keyof ArgMap>(funcs: Funcs, key: K, arg: ArgMap[K]) {
const func = funcs[key]; // Type Funcs[K]
func(arg);
}
function f3<K extends keyof ArgMap>(funcs: Funcs, key: K, arg: ArgMap[K]) {
const func: Func<K> = funcs[key]; // Error, Funcs[K] not assignable to Func<K>
func(arg);
}🙁 Actual behavior
Unexpected error in example above.
🙂 Expected behavior
No errors in example above.
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