| // Copyright 2016 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| 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"); |
| } |