Rust's "Other" Official Book (The Reference Guide)

I’ve used macro_rules! plenty of times, but recently I wanted to explore the full range of available fragment specifiers. I wasn’t trying to learn how to write a macro; I just wanted to know every single option available to me beyond the usual $x:expr or $y:ident.

I started where lots of others officially do: The Rust Programming Language (affectionately known as “The Rust Book”). But while The Rust Book is excellent, it doesn’t dive deep into the core language specification.

That is when I realized that Rust actually hosts two different “books” on the exact same domain. They are just a directory change away from one another:

1. The Rust Book (The Tutorial)

https://doc.rust-lang.org/book/

• Goal: Teaches you Rust from first principles. It focuses on building an intuitive understanding of “how Rust wants you to think.”
• Use it for: Learning ownership, borrowing, traits, and getting productive with Cargo.

2. The Rust Reference (The Specification)

https://doc.rust-lang.org/reference/

• Goal: Defines what Rust is. It describes the grammar, strict syntax rules, and edge cases. It is dry, precise, and exhaustive.
• Use it for: Looking up exact rules (like macro matchers), operator precedence, and memory models.

By the way, if you are looking for the exact definitions of macro metavariables (like I was), they are defined in the Reference here: https://doc.rust-lang.org/reference/macros-by-example.html#metavariables