## extern crate In source code of some libraries, I see extern crate. I cannot use it in my code, how does it work? https://doc.rust-lang.org/reference/items/extern-crates.html > An extern crate declaration specifies a dependency on an external crate. ## Procedural Macros https://doc.rust-lang.org/reference/procedural-macros.html - [Function-like macros](https://doc.rust-lang.org/reference/procedural-macros.html#function-like-procedural-macros) - custom!(...) - [Derive macros](https://doc.rust-lang.org/reference/procedural-macros.html#derive-macros) - #[derive(CustomDerive)] - [Attribute macros](https://doc.rust-lang.org/reference/procedural-macros.html#attribute-macros) - #[CustomAttribute]