The Complete Rust Programming Reference Guide

Types of macros

There are different forms of macros in Rust. Some allow you to call them like functions, while others allow you to conditionally include code, depending on compile-time conditions. Another class of macros allows you to implement traits on methods at compile time. They can be broadly divided into two forms:

• Declarative macros: These are the simplest form of macros. These are created using macro_rules!, which itself is a macro. They provide the same ergonomics of a calling a function, but are easily distinguished by a ! at the end. They are the go-to approach for writing quick small macros within a project. The syntax for defining them is very similar to how you would write match expressions. They are called declarative in ...