Can't assign never as object value to conditional type

[vpzomtrrfrt]

🔎 Search Terms

"never conditional not assignable"

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about never

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.4.0-dev.20231128#code/C4TwDgpgBAYg9nAPAFQHxQLxQN4DcCGANgK4QBcUyAvgNwBQokUAQvgE4rpbJQQAewCADsAJgGcoxURABmASyEQRUAPw4CJcpSpQKeIqQrV6dGVIDGwOXCFQARu04AKAJQ46UT1HM2xwKHwU8EhomOoGWgAMUPgSirgQbLQeXj5CflAgFKwcoVj6mhTRsVDxicle3r7+AF7ZjnlQxXEQCWz0VEA

💻 Code

type Foo<T> = {value: T};
type Bar<T> = T extends undefined ? {value: T} : {value: T};

function bar<T>() {
    const x: Foo<T> = {value: 0 as never};
    const y: Bar<T> = {value: 0 as never};
    const z: Bar<T> = 0 as never;
}

🙁 Actual behavior

Type '{ value: never; }' is not assignable to type 'Bar<T>'. on the const y line, despite the fact that Bar should be equivalent to Foo

🙂 Expected behavior

I expect to be able to assign never to everything

Additional information about the issue

No response

[MartinJohns]

Resolving of conditional types involving unbound type arguments is deferred. The compiler doesn't know what type T is, so it can't resolve the conditional type.

This should really be added to the FAQ, given how often this gets reported (a lot).

I expect to be able to assign never to everything

You are. But in the case of y you're not trying to assign never, you're trying to assign an object.

[RyanCavanaugh]

Duplicate #51488, others

[typescript-bot]

This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.