Box<Iterator<Item=&Trait>>

box_iterator.rs

use std::slice::Iter;

trait Test {
    fn hello(&self);
}

impl Test for i32 {
    fn hello(&self) {
        println!("i32 {}", self);
    }
}

struct TestIter<'a, T: 'a> {
    it: Iter<'a, T>,
}

impl<'a, T> Iterator for TestIter<'a, T>
    where T: Test + 'a
{
    type Item = &'a Test;
    
    fn next(&mut self) -> Option<Self::Item> {
        self.it.next().map(|i| i as &Test)
    }
}

impl<'a, T> TestIter<'a, T> {
    fn new(it: Iter<'a, T>) -> TestIter<'a, T> {
        TestIter {
            it: it
        }
    }
}

enum Tata<'b> {
    Shipo,
    Lata(Box<Iterator<Item=&'b Test> + 'b>)
}

fn test<'b>(test: &'b [i32]) -> Tata {
    //let a: Iter<'b, i32> = test.iter();
    //let b: TestIter<'b, i32> = TestIter::<'b, i32>::new(a);
    Tata::Lata(Box::new(TestIter::<'b, i32>::new(test.iter())) as Box<Iterator<Item=&'b Test>>)
}

fn main() {
    let a = [1, 2, 3i32];
    let b = Tata::Shipo;
    match test(&a) { 
        Tata::Lata(i) => {
            for t in i {
                t.hello();
            }
        },
        _ => (),
    }
    ()
}