Nullish coalescing operator but for conditional types about typescript HOT 2 OPEN

You can just define your own utility type like type OrElse<A, B, C> = [A] extends [B] ? A : C and use that. TS is unlikely to add new syntax if utility types can serve the same purpose, even if you'd prefer to see A extends B ?? C and not OrElse<A, B, C>.

Also, bikeshedding syntax: ?? doesn't seem to have the same meaning in your suggestion as it does in JS. Where is the "nullishness" here? Maybe if B is {}? I'd expect a type like A??C to evaluate to A unless it is nullish, and then C otherwise, so that string ?? number is string, but null ?? number is number. Since that's not what you're suggesting, the particular syntax would be misleading.

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To not repeat yourself, you can use infer R extends as a workaround. Not sure what your real-world code looks like but this may work.

type Foo<T> = Bar<
    [Some<Really<Deep<Complex<Type<Utility<T>>>>>>] extends [infer R extends readonly unknown[]]
        ? R
        : never
>;

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