30 lines
594 B
Rust
30 lines
594 B
Rust
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");
|
|
}
|