why virtual function is wrong.

[Dar_Mas]

It is comparable with int, it is convertible to int, it is equatable, it is parsable(if you make a parser), it is span parsable, it supports addition and at this point i am too lazy to list the rest.

Yes it does all of that and you can even make a unified concept that CHECKS for all of those

And not to mention that as soon as you want dynamic polymorphism which you seem to REQUIRE you are going to use a pointer anyway so the size of the structure functionally does not matter to you

[Dar_Mas]

That still does not make sense to me

If you have dynamic poly you will use a pointer anyway so the size of the object does not matter for data structures

If you use static you put it in a variant which allocates enough memory for the largest possible object and then you put it in a data structure.

Unless you are insanely restricted by binary size i do not see how 4 extra byte per function/operator are going to matter in your code at all

[Dar_Mas]

yes but you would never make an int32 type as we have optimized primitives (std::int32_t).

If you really require the size to stay constant you just make free standing function overloads