use std::fmt::Display;

trait Show {
    fn show(&self) -> String;
}

impl<T: Display> Show for T {
    fn show(&self) -> String {
        format!("{}", &self)
    }
}

fn blah_vtable<F>(f: F, x: i32, y: bool, z: char) -> String
where
    F: Fn(&dyn Show) -> String,
{
    format!("{} {} {}", f(&x), f(&y), f(&z))
}

fn main() {
    println!("Hello, world!");
}