pub trait Backend {
    fn add(&self, op1: i32, op2: i32) -> i32;
}

struct MyBackend {}
impl Backend for MyBackend {
    fn add(&self, op1: i32, op2: i32) -> i32 {
        op1 + op2
    }
}

struct Basic {
    backend: Box<dyn Backend>
}
use std::ops::Deref;
impl Deref for Basic {
    type Target = Box<dyn Backend>;
    fn deref(&self) -> &Self::Target {
        &self.backend
    }
}

fn main() {
    let x = Basic {
        backend: Box::new(MyBackend {})
    };
    println!("{}", x.add(1, 2));
}