Unique constraint for TypeScript generics

Question

The following example should not be considered as a real use case. It should only help to understand the question.

function myFunc<T1 extends string, T2 extends string>(s1: T1, s2: T2): string {
  return "";
}

Is it possible to ensure that T1 !== T2, hence that it is not possible to call myFunc like myFunc("MyValue", "MyValue")?

lukmac · Accepted Answer · 2022-03-31 21:20:29Z

4

I think I figured it out.

function myFunc<T1 extends string, T2 extends string>(s1: T1, s2: T2 extends T1 ? never : T2): string {
  return "";
}

answered Mar 31, 2022 at 21:20

lukmac

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2 Comments

Color me surprised, that totally works. Was about to comment that it's not possible until I tried it myself just now. Learned something new today.

@Andrew How does this color you: github.com/sno2/bf