Derive macros for automatic trait implementations

Rust's #[derive] attribute auto-generates trait implementations for common traits like Debug, Clone, PartialEq, and Serialize. This eliminates boilerplate and ensures consistency. For example, #[derive(Debug)] generates a debug formatter that prints all fields. Custom derive macros (from crates like serde or thiserror) can generate complex code based on the struct definition. I derive Debug and Clone on almost every type during development. For production, I add Serialize and Deserialize for data that crosses boundaries. Derive macros are a form of compile-time metaprogramming that keeps code DRY without runtime cost. It's one of the features that makes Rust feel high-level despite being systems-focused.