> But such a type doesn't really mention the lifetimes of whatever it captures, so in practice it doesn't work well in Rust. It can: Box<dyn Fn(Arg) -> R + 'a>

> But such a type doesn't really mention the lifetimes of whatever it captures, so in practice it doesn't work well in Rust. It can: Box<dyn Fn(Arg) -> R + 'a> This is just the general syntax for any trait object with a lifetime.