40 lines
1.1 KiB
Rust
40 lines
1.1 KiB
Rust
// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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macro_rules! log {
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( $ctx:expr, $( $args:expr),* ) => {
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if $ctx.trace {
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//~^ ERROR attempted access of field `trace` on type `&T`, but no field with that name
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println!( $( $args, )* );
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}
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}
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}
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// Create a structure.
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struct Foo {
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trace: bool,
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}
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// Generic wrapper calls log! with a structure.
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fn wrap<T>(context: &T) -> ()
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{
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log!(context, "entered wrapper");
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//~^ in this expansion of log!
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}
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fn main() {
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// Create a structure.
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let x = Foo { trace: true };
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log!(x, "run started");
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// Apply a closure which accesses internal fields.
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wrap(&x);
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log!(x, "run finished");
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}
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