#[derive] (Rust)
Rust-attribute som auto-implementerar traits för structs/enums. #[derive(Debug, Clone, PartialEq, Serialize)]. Standardway att avoid boilerplate för common-trait-impls. Pioneered Rust-ergonomics.
Built-in derivable: Debug, Clone, Copy, PartialEq, Eq, Hash, Default, Ord, PartialOrd. Library-defined: serde (Serialize/Deserialize), thiserror (Error), schemars (JsonSchema). Custom derive-macros: crate-authors can-define-own derive-macros via proc-macro-crate. Modern Rust-ekosystem: serde+thiserror+anyhow är universally-used derived-traits. Compile-time-cost: each derive expands till substantial-code, contributing till Rust:s slow-compile-times. Modern-alternative: hand-written-impls för performance-critical-code, derive för everything else.