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Generic return type (T[K]) is intersection among all properties of T instead of union #54901
Description
Bug Report
🔎 Search Terms
conditionally generic return type, union vs intersection, valueof etc
🕗 Version & Regression Information
- This changed between versions 3.3.3 and 3.5
⏯ Playground Link
Playground link with relevant code
💻 Code
export interface ConfigA {
user: string
}
export interface ConfigB {
[key: string]: number | string | boolean
}
export interface Config {
A?: ConfigA
B?: ConfigB
}
export class ConfigClass {
config: Config = {}
get(key: keyof Config) {
return this.config[key]
}
}
type ValueOf<T> = T[keyof T]
const config = new ConfigClass()
function a<K extends keyof Config>(key: K): Config[K] {
return config.get(key)
}🙁 Actual behavior
Type 'ConfigA | ConfigB | undefined' is not assignable to type 'Config[K]'.
Type 'ConfigA' is not assignable to type 'Config[K]'.
Type 'ConfigA' is not assignable to type 'ConfigA & ConfigB'.
Type 'ConfigA' is not assignable to type 'ConfigB'.
Index signature for type 'string' is missing in type 'ConfigA'.
🙂 Expected behavior
I would expect no error of returning config.get(key) within function a
Activity
olivermrose commentedon Jul 6, 2023
getneeds to be generic; otherwise, the return type is essentiallyConfig[keyof T].taozhou-glean commentedon Jul 7, 2023
thanks! But even with
Config[keyof T], should not it beConfigA | ConfigBinstead ofConfigA & ConfigB?The example is a simplified case just for the minimum repro, in reality we are having this issue with a IPC proxy, and the final
xx.getis also generic, but I am getting exact same error, maybe I should update the playground with a more realistic case.fatcerberus commentedon Jul 7, 2023
It’s a side effect of #30769.
typescript-bot commentedon Jul 9, 2023
This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.