[rust-dev] Macros expanding to multiple statements

Huon Wilson dbau.pp at gmail.com
Sat Jan 11 18:43:54 PST 2014


That test is for multiple *items*, not statements.

For the moment, you just have to wrap the interior of a macro expanding 
to an expression in a set of braces, so that it becomes a single statement.

macro_rules! my_print(
     ($a:expr, $b:expr) => (
         {
             println!("{:?}", a);
             println!("{:?}", b);
         }
     );
)

Multi-statement macros are covered by 
https://github.com/mozilla/rust/issues/10681 .


Huon


On 12/01/14 13:40, Ashish Myles wrote:
> Rust 0.9 indicates that support for expansion of macros into multiple 
> statements is now supported, and the following example from the test 
> suite works for me.
> https://github.com/mozilla/rust/blob/master/src/test/run-pass/macro-multiple-items.rs
>
> However, I receive an error for the following code
>
> #[feature(macro_rules)];
>
> macro_rules! my_print(
>     ($a:expr, $b:expr) => (
>         println!("{:?}", a);
>         println!("{:?}", b);
>     );
> )
>
> fn main() {
>     let a = 1;
>     let b = 2;
>     my_print!(a, b);
> }
>
> (Note that the ^~~~~~~ below points at println.)
>
> $ rustc macro_ignores_second_line.rs <http://macro_ignores_second_line.rs>
> macro_ignores_second_line.rs:6:9: 6:16 error: macro expansion ignores 
> token `println` and any following
> macro_ignores_second_line.rs:6 <http://macro_ignores_second_line.rs:6> 
> println!("{:?}", b);
>                                        ^~~~~~~
> error: aborting due to previous error
> task 'rustc' failed at 'explicit failure', 
> /home/marcianx/devel/rust/checkout/rust/src/libsyntax/diagnostic.rs:75 
> <http://diagnostic.rs:75>
> task '<main>' failed at 'explicit failure', 
> /home/marcianx/devel/rust/checkout/rust/src/librustc/lib.rs:453 
> <http://lib.rs:453>
>
>
> What's the right way to do this?
>
> Ashish
>
>
> _______________________________________________
> Rust-dev mailing list
> Rust-dev at mozilla.org
> https://mail.mozilla.org/listinfo/rust-dev

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