| macro_rules! log { |
| ( $ctx:expr, $( $args:expr),* ) => { |
| if $ctx.trace { |
| //~^ no field `trace` on type `&T` |
| println!( $( $args, )* ); |
| } |
| } |
| } |
| |
| // Create a structure. |
| struct Foo { |
| trace: bool, |
| } |
| |
| // Generic wrapper calls log! with a structure. |
| fn wrap<T>(context: &T) -> () |
| { |
| log!(context, "entered wrapper"); |
| //~^ in this expansion of log! |
| } |
| |
| fn main() { |
| // Create a structure. |
| let x = Foo { trace: true }; |
| log!(x, "run started"); |
| // Apply a closure which accesses internal fields. |
| wrap(&x); |
| log!(x, "run finished"); |
| } |