a day ago
- Macros in programming are code that writes code, typically at compile-time, evolving from simple text-substitutions in early assemblers.
- C macros (like #define) are prone to bugs due to simple string-replacement, leading to issues with operator precedence and side effects.
- Modern languages like Lisp introduced macros operating on abstract syntax trees, and Scheme added hygienic macros to prevent unintended variable capture.
- Rust macros are hygienic and have a type system, allowing patterns with typed arguments (e.g., expr, ident, ty) and repetition for boilerplate generation.
- Rust macros support recursive invocations, enabling compile-time computations like the Collatz number or binary conversion.
- Advanced techniques include token munching, building memory structures (e.g., using brackets), and treating collections as single token trees for efficient processing.
- Rust macros can be used for practical tasks like implementing traits for tuples, with hygienic variable creation preventing naming collisions.
- Best practices recommend breaking complex macros into smaller, manageable pieces (e.g., using traits and multiple macros) rather than creating monolithic implementations.