I should have made that caveat: if X doesn't need all of the bits that it has, then yes, you can do this. But there is no way to know that this is the case for

I should have made that caveat: if X doesn't need all of the bits that it has, then yes, you can do this. But there is no way to know that this is the case for a generic type parameter, you can only do this if you know the semantics of the specific type you are dealing with, like the language does for pointer types. I should also point out that in languages which support both, Option(int*) is a valid construct, and Some(nullptr) is thus not the same thing as None. There could even be valid reasons for needing to do this, such as distinguishing between the JSON objects {} and {"abc": null}. So you can't even use knowledge of built-in types to special-case your generic Option implementation. Even Option(Option(bool)) should be able to represent at least 4 distinct states, not 3: None, Some(None), Some(Some(true)), Some(Some(false)).