trait Trait1 {
    fn is_id(&self, id: usize) -> bool;
}
trait Trait2{}

struct Core {
    objs: Vec<obj1>,
    diff_objs: Vec<obj2>,
}

struct obj1 {
    stuff: String,
    id: usize,
}

impl Trait1 for obj1 {
    fn is_id(&self, id: usize) -> bool { self.id == id }
}

impl Trait2 for obj1 {}

struct obj2 {
    other_stuff: String,
    id: usize,
}

impl Trait1 for obj2 {
    fn is_id(&self, id: usize) -> bool { self.id == id }
}

impl Trait2 for obj2 {}

// This could live in impl Core maybe?
fn return_trait<T: Trait1 + Trait2>(core: &Core, id: usize) -> Result<T, String> {
    for obj in core.objs.iter() {
        if obj.is_id(id) { return Ok(obj); }
    }
    for obj in core.diff_objs.iter() {
        if obj.is_id(id) { return Ok(obj); }
    }
    Err("Couldn't find ID".to_string())
}

fn main() {

}