struct Scope<'a>
{
    parent: Option<&'a mut Scope<'a>>,
	// Some data here
}

impl<'a> Scope<'a>
{
    fn new() -> Scope<'a>
    {
        Scope {
            parent: None,
        }
    }

    fn child(&'a mut self) -> Scope<'a> // lifetimes here
    {
        Scope {
            parent: Some(self),
        }
    }
}

fn foo(scope: &mut Scope)
{
    bar(scope);
    bar(scope);
}

fn bar(scope: &mut Scope)
{
    scope.child();
}

fn main() -> () {
    let mut scope = Scope::new();

    foo(&mut scope);
}