Methods with generic properties in a class cannot be assigned to unknown.

[LiST-GIT]

🔎 Search Terms

generic
method

🕗 Version & Regression Information

v5.4.4

⏯ Playground Link

https://www.typescriptlang.org/play?#code/MYGwhgzhAECCA8AVAfNA3gWAFDV9AJgKahgBOh0AZgK4B2wAXNABQBuYI1hTiAlNAF5UrAPYBLfAG5seaMA4hm-TDll5gI2hAAu0MEwR0A1rREB3WqgHRtACzERpq3AF9sbrEA

💻 Code

class A<T> {
    declare func: (value: T) => void;
    call() {
        const a: A<unknown> = this;
           // ^
    }
}

Type 'this' is not assignable to type 'A<unknown>'.
  Type 'A<T>' is not assignable to type 'A<unknown>'.
    Type 'unknown' is not assignable to type 'T'. // <-----
      'T' could be instantiated with an arbitrary type which could be unrelated to 'unknown'.

🙁 Actual behavior

Judging from the error message, could it be that the comparison was written in reverse?

🙂 Expected behavior

Any value can be assigned to unknown.

Additional information about the issue

No response

[jakebailey]

This error is correct. Say you have an A<number>. It must be the case that you can only pass numbers into its func. But if you assign an A<number> to A<unknown>, now func can accept unknown, which is anything, which violates what func of A<number> expects.