[ncmncm]

Each is easier than the other, depending on where you look and where you come from.

But it is a fair bet that changes to C++ code to implement a point performance optimization will be smaller than the same sort of change would be for Rust code. For the latter, you are likely to need to re-architect that part of the system some to get your optimization and still satisfy the borrow checker. Having a borrow checker that demands satisfaction is a virtue, but there is no denying it adds cost in the small, where we're talking about, notwithstanding that such cost may be paid back at the system level.