Examples of generics needed

Minimal code to reproduce the problem

code:ts

type X = "A" | "B";

const f = (x: X): X => (x);

const a: "A" = f("A"); // error

error

Type 'X' is not assignable to type '"A"'.

Type '"B"' is not assignable to type '"A"'

solution

code:ts

const f = <T extends X>(x: T): T => (x);

const a: "A" = f("A"); // ok

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