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30 lines
594 B
Rust
30 lines
594 B
Rust
macro_rules! log {
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( $ctx:expr, $( $args:expr),* ) => {
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if $ctx.trace {
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//~^ no field `trace` on type `&T`
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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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