Bignum arithmetic actually is pretty simple in Rust if you use the right library. Rug[0] makes using bignums look almost just like using native numbers through operator overloading.
The operator overloading is nice but you still get smacked in the face right away by the borrow checker. Simple stuff like this won't compile ("use of moved value"):
let a = Integer::from(10);
let b = a + a;This would work if `Integer` would implement the `Copy` trait. But I guess that type is heavy enough for it to be too expensive, therefore forcing you to explicitly call `clone()`.
That `Integer` type can't implement `Copy` because it manages a resource, meaning you can't just do a simple memcpy of the type.
Bignum arithmetic is an example of the latter. You want to just work with numbers, and in Python you can, but in Rust you must clutter your code with lifetimes and borrows and clones.
Swift's plan to allow gradual, opt-in lifetime annotations seems really interesting, if it works.