Yes, you can do this in typescript, but you can also lie about it in typescript. To do it provably, you would construct a function that accepted the more generi

Yes, you can do this in typescript, but you can also lie about it in typescript. To do it provably, you would construct a function that accepted the more generic version and then, using type assertions (ie the typescript compiler infers the type from declared runtime behavior), it would return a narrowed type. If one caller passes our type narrower with {age:F<u32>} then the return value of the function will be narrowed to that type, but a broader criteria can still be specified for the generic instance.