Deref example

playground.rs

use std::ops::Deref;
use rand; // 0.7.3
use rand::Rng;

#[derive(Debug, PartialEq)]
struct Wrap<T> {
    inside: T
}

impl<T> Wrap<T> {
    fn new(inside: T) -> Wrap<T> {
        Wrap {
            inside
        }
    }
}

impl<T> Deref for Wrap<T> {
    type Target = T;

    fn deref(&self) -> &T {
        &self.inside
    }
}

fn make_a_string_with(string: &str) -> String {
    let mut s = String::new();
    s.push_str(string);

    let mut rng = rand::thread_rng();
    let r = rng.gen_range(0, 100);
    for _ in 0..r {
        s.push_str("!");
    }
    s
}

fn main() {
    let string = String::new("Hello World");
    let wrap = Wrap::new(string);
    let result = make_a_string_with(&wrap); // deref coercions
    
    println!("len: {}, string: {}", result.len(), result);
}