Rust by Example中文

9 macro_rules!

Rust provides a powerful macro system that allows metaprogramming. As you've seen in previous chapters, macros look like functions, except that their name ends with a bang !, but instead of generating a function call, macros are expanded into source code that gets compiled with the rest of the program.

Macros are created using the macro_rules! macro.

// This is a simple macro named `say_hello`. macro_rules! say_hello { // `()` indicates that the macro takes no argument. () => ( // The macro will expand into the contents of this block. println!("Hello!"); ) } fn main() { // This call will expand into `println!("Hello");` say_hello!() }