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.... 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.
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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.... 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.
Swift uses ARC to mean automatic, and its use comes from Objective-C's ARC.
Huh, the Nim blog post appears to be wrong, then, or I misunderstood it.