Shared via Rust Playground

playground.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
        }
    }
}

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

fn main() {
    let a = &[1, 2, 3i32];
    for t in test(a) {
        t.hello();
    }
}