We already saw that we can write #[derive(Copy, Debug)] on any struct, enum, or union type to get the Copy and Debug traits implemented for it, but this auto-derive feature is limited only to a few built-in traits in the compiler. With derive macros or macros 1.1, you get the ability to derive your own custom trait on any struct or enum or union type, thereby reducing the amount of boilerplate code that you would have written by hand. This may seem like a niche use case, but it is the most used procedural macro form, which high performance crates such as serde and diesel use. The derive macros only apply to data types such as structs, enums, or unions. Creating a custom derive macro for implementing a trait on a type requires the following steps:
- First, you need your type and the trait that you want to implement on the type. These can come from any crate, either...