If you access the bool through a long path maybe.

  foo.bar().baz[expensive()].qux.toggle();

This gives me the same feeling as when I saw Rust's map Entry API

https://doc.rust-lang.org/std/collections/hash_map/enum.Entr...

    let mut map: HashMap<&str, u32> = HashMap::new();
    map.entry("poneyland").or_insert(3);
    assert_eq!(map["poneyland"], 3);

Alright, I'm convinced, that makes a lot of sense.

That's the main reason for me as well

cant you just do

    foo.bar().baz[expensive()].qux ^= true;