Rust 1.28.0-dev

Macros

There is a new edition of the book and this is an old link.

While functions and types abstract over code, macros abstract at a syntactic level.

macro_rules! five_times {
    ($x:expr) => (5 * $x);
}

fn main() {
    assert_eq!(25, five_times!(2 + 3));
}Run

Here are the relevant sections in the new and old books:

• In the second edition: Appendix D — Macros
• Rust By Example: Macros
• In the Rust Reference: Ch 3.1 — Macros by Example
• In the first edition: Ch 3.34 — Macros