Mastering Rust - Second Edition

Attributes

An attribute is an annotation on an item in Rust code. Items are top-level language constructs in a crate such as functions, modules, structs, enums, and constant declarations, and other things that are meant to be defined only at the crate root. Attributes are usually compiler built-ins, but can also be created by users through compiler plugins. They instruct the compiler to inject extra code or meaning for the item that appears below them, or for the module if they apply to a module. We'll cover more on these in Chapter 7, Advanced Concepts. For the sake of keeping things in scope, we will talk about two forms of attributes here:

• #[<name>]: This applies per item and usually appears above them in their definition. For example, ...