quote
cargo-expand
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| quote | cargo-expand | |
|---|---|---|
| 3 | 16 | |
| 1,219 | 2,435 | |
| - | - | |
| 7.3 | 9.0 | |
| 11 days ago | 9 days ago | |
| Rust | Rust | |
| Apache License 2.0 | Apache License 2.0 |
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quote
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C++ vs. Rust Build Times
A surprising source of slow compile times can be declarative macros in Rust [0].
I believe the core of the problem is that it has to reparse the code to pattern match for the macro.
One egregious patter is tt-munchers [1] where your macro is implemented recursively, requiring it to reparse the source on each call [2].
In one of my projects, someone decided to wrap a lot of core functions in simple macros (ie nt tt-munchers) to simplify the signatures. Unlike most macros which are used occasionally and have small inputs, this was a lot of input. When I refactored the code, I suspect dropping the macros is the reason CI times were cut in half and a clean `cargo check` went from 3s to 0.5s.
[0]: https://nnethercote.github.io/2022/04/12/how-to-speed-up-the...
[1]: https://veykril.github.io/tlborm/decl-macros/patterns/tt-mun...
[2]: https://github.com/dtolnay/quote/blob/31c3be473d0457e29c4f47...
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Is generating code from JSON a good macro use case?
In the build.rs, call your code generation function (probably in a separate crate added in build-dependencies). This function will read your input files, and use something like quote to generate code.
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Any good resources for learning Rust macros?
Or you can pair them with crates like syn, and quote for quasi-quoting, and then it's easy to make transformations on the AST of Rust input code. A lot of libraries do this for code-generation and hiding away a lot of complexity (example wasm-bindgen).
cargo-expand
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What is Rust doing behind the scenes?
It's been superseded by https://github.com/dtolnay/cargo-expand
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Why dereferencing coercion is not used here?
Try installing cargo expand, it's useful to see how macros eventually get expanded. For example, if you run cargo expand on the following code
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Procedural Macros are really hard to understand
You can use cargo expand to see what your code expands to: https://github.com/dtolnay/cargo-expand
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[blog] Rust should own its debugger experience
Not too familiar with macros but does cargo-expand do what you want or did you mean something else?
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Help me understand the borrowing and moving variable concept!
Yes. You can use Tools > Expand Macro on the playground or install and run cargo-expand to see what the macro expands to. It just adds a & before the argument.
- Advanced Metaprogramming in C: A select statement
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How does declaring variables in macros work
cargo expand
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How to see macro's source code in crate?
Along with what others are saying, there is also cargo expand which can show you what code a macro generates
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How does Rust Python ffi work?
Something that may help you understand code with magic proc macros is this utility. It's basically a wrapper around a Rust compiler flag that allows you to expand macros for a file.
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How does libtest know which functions are marked with #[test]?
You can use https://github.com/dtolnay/cargo-expand to examine how it works.
What are some alternatives?
proc-macro-workshop - Learn to write Rust procedural macros [Rust Latam conference, Montevideo Uruguay, March 2019]
saito-rust - A high-performance (reference) implementation of Saito in Rust
Bytecode - A Rust proc-macro crate which derives functions to compile and parse back enums and structs to and from a bytecode representation
component-keycloak - Commodore Component for Keycloak
lol-html - Low output latency streaming HTML parser/rewriter with CSS selector-based API
darling - A Rust proc-macro attribute parser
rust - Empowering everyone to build reliable and efficient software.
hickory - Command line tool for scheduling Python scripts
cargo-llvm-cov - Cargo subcommand to easily use LLVM source-based code coverage (-C instrument-coverage).
syn - Parser for Rust source code
rustviz - Interactively Visualizing Ownership and Borrowing for Rust