struct S1 {
  v: i32,
}

struct S2 {
  t: f64,
}

trait ShowMe {
  fn show(&self);
}

impl ShowMe for S1 {
  fn show(&self) {
    println!("I am an S1, and my value is {}", self.v)
  }
}

impl ShowMe for S2 {
  fn show(&self) {
    println!("I am an S2, and my value is {}", self.t)
  }
}
impl ShowMe for i64 {
  fn show(&self) {
    println!("I am a 64-bit integer, and my value is {}", self)
  }
}

fn f(v: &dyn ShowMe) {
  print!("Invoking show()... ");
  v.show()
}

fn main() {
  let a = S1{v:5};
  let b = S2{t:0.1};
  let c = 666;
  let t = 0;

  let mut v: &dyn ShowMe = if t == 0 { &a } else { &b };

  f(v);
  if t == 0 { v = &c };
  f(v);
}