It would be nice to have a method for getting the memory consumption of BigInts and BigUInts. In particular this crate is being used by RustPython, and the python spec requires builtins to implement a __sizeof__ method that returns the amount of memory used by an object in bytes. This is quite easy to calculate using std::mem::size_of_val, unfortunately it requires a reference to the underlying data Vec, which of course is not exposed by the BigInt api.

My proposal is to either:

1. Add a method for getting a reference to data or
2. Add a method for getting the size of BigInt/BigUInt

I would prefer the first option because it will support a lot more unforseen use cases.

See the discussion at RustPython/RustPython#1172