The name is confusing, but Nim's Arc is not the same as Rust's: https://nim-lang.org/blog/2020/10/15/introduction-to-arc-orc-in-nim.html https://nim-lang.org/bl

The name is confusing, but Nim's Arc is not the same as Rust's: https://nim-lang.org/blog/2020/10/15/introduction-to-arc-orc-in-nim.html https://nim-lang.org/blog/2020/10/15/introduction-to-arc-orc.... Rust (and apparently Swift) uses Arc to refer to atomic reference counting, whereas Nim's means automatic. There's still overhead, but it would be more comparable to Rust's Rc, I believe.