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// run-pass // ignore-pretty pretty-printing is unhygienic #![feature(decl_macro)] trait Tr { fn f(&self) -> &'static str { "This shouldn't happen" } } pub macro m($t:ty) { impl Tr for $t { fn f(&self) -> &'static str { "Run me" } } } struct S; m!(S); fn main() { assert_eq!(S.f(), "Run me"); }