---
source: https://iinventedlight.com/library/notes/rust-macros.md
title: "Macros in Rust: declarative and procedural"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "MIT OR Apache-2.0 (rust-lang/book; Copyright (c) 2010 The Rust Project Developers); additional cited sources under MIT OR Apache-2.0; prose restates cited source lines in own words"
license_family: rust-mit
attribution: "Summary by iinventedlight (AI-assisted). Sources: The Rust Project (The Rust Programming Language book), Macros, MIT OR Apache-2.0; Rust by Example (rust-lang/rust-by-example), macro_rules! - Rust By Example, MIT OR Apache-2.0. Notices: The Rust Programming Language book (rust-lang/book): Copyright (c) 2010 The Rust Project Developers; MIT OR Apache-2.0, used under MIT (https://github.com/rust-lang/book/blob/main/LICENSE-MIT). Rust by Example (rust-lang/rust-by-example): Copyright (c) 2014 Jorge Aparicio; MIT OR Apache-2.0, used under MIT (https://github.com/rust-lang/rust-by-example/blob/master/LICENSE-MIT)."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-09
status: published
approved_by: "Cole Withington, 2026-11-09 13:40 PT: \"Yes, publish all 15 Rust drafts\""
checked_on: 2026-11-09
as_of: 2026-11-09
confidence: medium
untested: "No Rust code was run for this note; only the fetched documentation pages were read."
category: coding-references
topic_area: "code-systems: Rust macros"
tags: [rust, macros, metaprogramming]
client: Librarian
sources:
  - id: S1
    title: "Macros"
    publisher: The Rust Project (The Rust Programming Language book)
    url: https://doc.rust-lang.org/book/ch20-05-macros.html
    accessed: 2026-11-09
    license: "MIT OR Apache-2.0"
  - id: S2
    title: "macro_rules! - Rust By Example"
    publisher: Rust by Example (rust-lang/rust-by-example)
    url: https://doc.rust-lang.org/rust-by-example/macros.html
    accessed: 2026-11-09
    license: "MIT OR Apache-2.0"
---
# Macros in Rust: declarative and procedural

**Answer:** Macros generate code from code (metaprogramming). Declarative macros are the form Rust programmers use most.

## macro_rules

Rust's macro system supports metaprogramming. Declarative macros are also called macros by example, `macro_rules!` macros, or simply macros.

## Claims

- id: C1
  claim: Macros are a way of writing code that writes other code.
  source: S1
  evidence: "macros are a way of writing code that writes other code, which is known as"
- id: C2
  claim: The most widely used form is the declarative macro.
  source: S1
  evidence: "The most widely used form of macros in Rust is the declarative macro."
- id: C3
  claim: Rust provides a powerful macro system that allows metaprogramming.
  source: S2
  evidence: "Rust provides a powerful macro system that allows metaprogramming."

## Sources

- [S1] Macros. The Rust Project (The Rust Programming Language book). https://doc.rust-lang.org/book/ch20-05-macros.html . License: MIT OR Apache-2.0. Accessed 2026-11-09.
- [S2] macro_rules! - Rust By Example. Rust by Example (rust-lang/rust-by-example). https://doc.rust-lang.org/rust-by-example/macros.html . License: MIT OR Apache-2.0. Accessed 2026-11-09.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted). Sources and notices: The Rust Programming Language book (rust-lang/book): Copyright (c) 2010 The Rust Project Developers; MIT OR Apache-2.0, used under MIT (https://github.com/rust-lang/book/blob/main/LICENSE-MIT). Rust by Example (rust-lang/rust-by-example): Copyright (c) 2014 Jorge Aparicio; MIT OR Apache-2.0, used under MIT (https://github.com/rust-lang/rust-by-example/blob/master/LICENSE-MIT). Text was condensed and changed from the originals.

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