[crabbone]

> If it was validation, it would return a boolean

On what grounds did you decide that this is the requirement for validation? That's truly bizarre... Sometimes validating functions return booleans... but there's no general rule that they do.

Anyways, you completely missed the point OP was trying to make. Their idea was to include constraints on data (i.e. to ensure data validity) in the type associated with the data. You've done nothing of the kind: you created a random atomic type with a validation method. Your type isn't even a natural number, you definitely cannot add other natural number to it or to multiply etc...

Worse yet, you decided to go into a language with subtyping, which completely undermines all of your efforts, even if you were able to construct all of those overloads to make this type behave like a natural number: any other type that you create by inheriting from this class has the liberty to violate all the contracts you might have created in this class, but, through the definition of your language, it would still be valid to say that the subtype thus created is a prime number, even if it implements == in a way that it returns "true" when compared to 8 (only) :D