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Double (exclusion) inference doesn't narrow union object #61075
Description
🔎 Search Terms
"double inference", "exclusion inference", "union object narrow"
🕗 Version & Regression Information
I observed this issue on versions
- 5.4.5
- 5.7.3
⏯ Playground Link
💻 Code
type Test = ({
check: 'resolved'
thing: number
} | {
check: 'loading' | 'errored'
thing: undefined
})
const foo: Test = {} as Test
if (foo.check === 'loading' || foo.check === 'errored') {
foo.check
// ^?
foo.thing
// ^?
} else {
foo.check
// ^?
foo.thing
// ^?
// `foo.check` is `'resolved'` here, but `foo.thing` is still `number | undefined`
}🙁 Actual behavior
foo.check` is `'resolved'` here, but `foo.thing` is still `number | undefined
This is impossible considering the type
type Test = ({
check: 'resolved'
thing: number
} | {
check: 'loading' | 'errored'
thing: undefined
})🙂 Expected behavior
I expected foo.thing to be of type number since foo.check is of type 'resolved'
Additional information about the issue
No response
Activity
[-]Double inference doesn't narrow union object[/-][+]Double (exclusion) inference doesn't narrow union object[/+]IllusionMH commentedon Jan 29, 2025
Duplicate of #56023, #31404 etc.
exoRift commentedon Jan 29, 2025
What is the original issue? Is this planned to be fixed?
exoRift commentedon Jan 30, 2025
I've devised a workaround for this issue which is to split the property's string union into an upper-level object union
https://www.typescriptlang.org/play/?ts=5.7.3#code/C4TwDgpgBAKhDOwoF4oG8CwAoKuoGMALCfAawC4oByAJwQHsAbANwgBMrs8phCBLAHYBzSgICuAWwBGEGtgC+UAD7oueIiQrVG9AIZtBQqsuqya9OhzW5ehymIFsIAM0HsF2bPnoDEUZ-T0lHB+qGiKuvCwCMCeWHzOUAAUAfQAdBpkKMioVDr6hsZKKqkZxFk5uWYW7FQAlKo4eKWZpNZQAPQdUAB6APztpbbC7V29A1iKEIzw0JhNuC3lbQud3f2DgWnDQqPrE-JxoJBQAOoWpLrmDmwojdytlLQMLLXtO6KSMnKTJklJ8weyye+QMwk4vxUgPUwNMNHMlgh8gaADJ7ngPlAbi43GwFHU4t5fEgpFdKOcaJdro47uEoJEzhcrvQbnEEslSTQyppsrlQYVlCpOdyKjk4Qjag1obhha09uN2sKdvKNr9prN0TKriKVtwxqruEr+CNVvqDtggA
MartinJohns commentedon Jan 31, 2025
He linked the original issue. It's marked as design limitation, so it's unlikely to be solved anytime soon.
typescript-bot commentedon Feb 10, 2025
This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.