在macro_rules中使用另一个宏而不需要生锈的“extern crate”

Question

Is there a way to "re-export" #[macro_use] extern crate similar to pub use so that users of a macro using macros do not have to manually add these dependent extern crate s?

The rest of the question is an example to illustrate.

In src/lib.rs , note that the id macro is using the lazy_static macro:

#[macro_export]
macro_rules! id {
    () => {
        lazy_static! {
            static ref NUMBER : std::sync::atomic::AtomicUsize =
                std::sync::atomic::AtomicUsize::new(0);
        }
        return NUMBER.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
    }
}

In examples/example.rs , we need an extern crate line for each macro, even though we're just using the id macro directly:

#[macro_use]
extern crate id_macro;
#[macro_use]
extern crate lazy_static;

fn new_id() -> usize {
    id!();
}

fn main() {
    println!("id {}", new_id()); // prints "id 0"
    println!("id {}", new_id()); // prints "id 1"
}

In the example, it would be great if the user of id_macro could use id! without knowing about lazy_static . Is there a way to "re-export" extern crate similar to pub use to make the following lines go away from the example?

#[macro_use]
extern crate lazy_static;

Answer 1

There is an unstable macro_reexport attribute.

However, Rust is working on making macros ( 2.0 ) behave like normal items that support pub use , so this attribute won't be stable and will become obsolete.