use async_trait_fn::async_trait; #[async_trait] trait Foo { async fn bar(&self, x: &str, y: &'_ str) -> &'static str; } struct S(String); #[async_trait] impl Foo for S { async fn bar(&self, x: &str, y: &'_ str) -> &'static str { if false { &self.0 } else if false { x } else { y } } } fn main() {}