//@ check-pass struct Indexable; impl Indexable { fn boo(&mut self) {} } impl std::ops::Index<&str> for Indexable { type Output = Indexable; fn index(&self, field: &str) -> &Indexable { self } } impl std::ops::IndexMut<&str> for Indexable { fn index_mut(&mut self, field: &str) -> &mut Indexable { self } } fn main() { let mut v = Indexable; let field = "hello".to_string(); v[field.as_str()].boo(); v[&field].boo(); // < This should work }