use std::any::TypeId;

struct Type {
    type_id: TypeId
}

struct Instance<'a> {
    t: &'a Type
}

impl <'a> Instance<'a>{
    fn new(t: &Type) -> Instance<'a> {
        Instance { // <-- how do I specify the runtime 'a of Instance here????
            t
        }
    }
}