[Manishearth]

You only need a Cell for a counter (not even an atomic). Cell has no overhead over C -- Cell turns off some optimizations that exist in Rust to give you a C-like type.

I've been programming in Rust and C++ codebases for a while now. In general I find that Rust lets you dance close to the line of unsafety without worrying, resorting to Arc/RefCell only when you have to. In contrast, most C++ codebases I have worked with make use of shared_ptr (or its equivalent) quite often, because the language doesn't give you the tools to thread scoped borrows safely through a chain of functions and have it stay safe in the face of future code changes.