For such problems we use the Opaque type from the nifty type-fest package. We use it for all of our id types (which are usually numbers) so we can't accidentall

For such problems we use the Opaque type from the nifty type-fest package. We use it for all of our id types (which are usually numbers) so we can't accidentally mix them. In your example it would be: type Age = Opaque<number, "Age"> And then you wouldn't be able to pass a random number to printAge