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T[K] should be never when T is never #23005
Description
Activity
type Example<T> = T extends Record<'a', string> ? T['a'] : never;
maybe?
That actually only works because of how conditional types work with type parameters. It distributes the condition over any unions, and
neveris treated as an empty union. So it actually isn't thatneveris failing the condition there, it's that the condition is never even tested. It would actually pass the condition and end up asanyif the condition is tested.You can see that's what is happening more clearly with something like
type Example2<T> = T extends Record<'a', string> ? true : false; type Result2 = Example2<never> // never instead of either true or false
And if you get rid of the distribution behavior by wrapping the two sides in
[]you can see you still getany:type Example3<T extends Record<'a', string>> = [T] extends [Record<'a', string>] ? T["a"] : never; type Result3 = Example3<never> // any
Reacted by hapood- locked as resolved and limited conversation to collaborators
on Oct 21, 2025
TypeScript Version: 2.9.0-dev.20180329
Search Terms:
indexed access type, index type never
Code
Expected behavior:
Type of
Result3to beneverActual behavior:
Type of
Result3isanyPlayground Link:
Link
Workaround
Now that #22042 is resolved this can be worked around with
Related Issues:
Similar to #22042. That was about type of
T[K]whenKwasneverwhile this is about whenTisnever.