#[derive(Default)]
struct Message {
    e: Option<*mut u8>
}

trait Owner {
    type Message: Default;
    fn produce_message(&self) -> Self::Message {
        Default::default()
    }
}

struct You;
struct Me;

#[derive(Default)]
struct YourMessage(Message);

#[derive(Default)]
struct MyMessage(Message);

impl Owner for You { type Message = YourMessage; }
impl Owner for Me  { type Message = MyMessage; }

impl Drop for YourMessage {
    fn drop(&mut self) {
        println!("drop YourMessage");
        println!("free(self.0.e)");
    }
}

impl Drop for MyMessage {
    fn drop(&mut self) {
        println!("drop MyMessage");
        println!("free_magic(self.0.e)");
    }
}

fn main() {
    let y = You;
    y.produce_message();

    let m = Me;
    m.produce_message();
    m.produce_message();
}