Implementing an RPN Calculator in Rust

A hands-on walkthrough of building an RPN (Reverse Polish Notation) calculator in Rust, exploring several Rust-specific concepts along the way. Starting from a basic working implementation, the author iterates through improvements: efficient command-line argument iteration without double-collecting, deep dive into how `collect()` and turbo fish syntax work with generics and associated types, using closures with `FnOnce` trait bounds to eliminate repeated operator code, and replacing `unwrap()` calls with proper `Result`-based error handling. The final implementation is clean, idiomatic Rust with good error messages.