> IMHO, most large Rust project will likely use RC or ARC types or use lots of clone calls. So performance wise it’s not gonna be too different than Nim or Swift or even D really.

I do not think so. My personal experience is that you can go far in Rust without cloning/Rc/Arc while not opting for unsafe. It is good to have it as default and use Rc/Arc only when (and especially where) needed.

Being curious I ran some basic grepping and wc on the Ion Shell project. It has about 2.19% of function declarations that use Rc or Arc in the definition. That is pretty low.

Naive grepping for `&` assuming most are borrows seems (excluding &&) to be 1135 lines. Clone occurs in 62 lines for a ratio of 5.4%. Though including RC and ARC with clones and that you get about 10.30% vs `&` or borrows borrows. That's assuming a rough surrogate Rc/Arc lines to usages of Rc/Arc's.

For context doing a grep for `ref object` vs `object` in my companies Nim project and its deps gives a rate of 2.92% ref objects vs value objects. Nim will use pointers to value objects in many functions. Actually seems much lower than I'd would've guessed.

Overall 2.19% of Rust funcs in Ion using Rc/Arc vs 2.92% of my Nim project types using refs vs object types. So not unreasonable to hold they have similar usage of reference counting vs value types.