Boost Multiprecision [0] is an example of such a library type. It offers a compile-time arbitrarily wide integers (with predefined types up to 1024 bits) and a

Boost Multiprecision [0] is an example of such a library type. It offers a compile-time arbitrarily wide integers (with predefined types up to 1024 bits) and a C++ wrapper around the GMP or MPIR libraries, which supports arbitrary sizes at runtime (not sure how it's implemented, but probably on top of an array of ints or BCD (binary-coded decimals)). C++ has had `optional` and `variant` since (I think) C++11, maybe 14. I don't think `any` made the cut. All of these types originated (for C++ standardization) in Boost, as well. I'd caution against using `any`, though. From personal experience, the runtime overhead is quite high, and holding any non-none type is a dynamic allocation. Performance is far better with `variant` at the development cost of needing to know all the types you're going to support at compile-time. [0] https://www.boost.org/doc/libs/1_72_0/libs/multiprecision/doc/html/index.html https://www.boost.org/doc/libs/1_72_0/libs/multiprecision/do...