I'm looking for something like this...
type B = a ? 'apple' | 'grape' | 'orange' : 'apple' | 'grape'; // Of course, ERROR!
const x = (a: boolean, b: B) => console.log('foo')
How can I implement this? Is it possible in Typescript?
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I think you're looking for genericsVLAZ– VLAZ2022-02-25 09:47:24 +00:00Commented Feb 25, 2022 at 9:47
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1 Answer
You can indeed. To do this, you'll need to use generics and conditional types. Like this:
type Type1 = "apple" | "grape" | "orange";
type Type2 = "apple" | "grape";
const x = <A extends boolean>(a: A, b: A extends true ? Type1 : Type2) =>
console.log("foo");
x(false, "orange"); // error
x(true, "orange"); // no error
