use std::ops::Index;

struct Test;
struct Container(Test);

impl Test {
    fn test(&mut self) {}
}

impl<'a> Index<&'a bool> for Container {
    type Output = Test;

    fn index(&self, _index: &'a bool) -> &Test {
        &self.0
    }
}

fn main() {
    let container = Container(Test);
    let mut val = true;
    container[&mut val].test(); //~ ERROR: cannot borrow data
}